Sometime in the next two weeks, you'll pull the big pot down off the top shelf. The nights are cooler now. Soup starts to sound right again.

And right on cue, the first coughs of the season show up at church, at the grocery store, at your grandkid's school. Out come the fizzy tablets and the gummy bottles. You spend twenty dollars, maybe thirty, on packets that promise to keep you going.

But the pot on your stove can do some of that work. One mushroom has a stack of blood tests behind it. It costs a few dollars. And it makes the best soup you'll eat all fall...

Here's the pot.

What you need: One pound fresh shiitake mushrooms. Six dried shiitake. An onion. A spoon of olive oil. Six cups of water. Two big handfuls of spinach or kale. Salt and pepper.

How: Soak the dried caps in 2 cups of hot water for 20 minutes. Pull the stems off the fresh caps and set them aside. Slice the caps. Chop the onion and soften it in the oil for 5 minutes. Add the fresh caps and let them cook until they give up their water and turn brown, about 8 minutes. Slice the soaked caps and toss them in with the stems. Pour in the soaking water, but leave the last spoon of grit in the bowl. Add 4 more cups of water. Simmer for 20 minutes. Fish out the stems. Stir in the greens for the last 2 minutes, then salt to taste.

The fresh caps are the star. Dried ones bring a deep, meaty taste, and their soaking water turns plain water into broth. An onion gives the pot a sweet base. Oil lets the caps brown instead of steam. And the greens go in last, so they stay bright.

That twenty-minute simmer isn't for flavor, though. It's the one rule of this mushroom, and I'll get to it. First, meet the man who worked out how to grow it...

Scientists have linked one common drink to skyrocketing rates of Alzheimer’s disease: it carries shocking levels of a toxic mineral present in many patients’ brains.

That mineral builds in the brain over time, killing off a molecule that keeps your memories intact. Can you guess which one it is?

▸  Black Coffee (Colombian Beans)

▸  White Wine (Chardonnay Grapes)

▸  Diet Soda

▸  Tap Water

▸  Beer

If you think it’s the drinks that contain alcohol, you might want to think again.

About 900 years ago, in the steep hills of what is now Zhejiang province in China, a young woodcutter named Wu Sangong saw something odd. Brown mushrooms kept coming up along the axe cuts in fallen logs. The more cuts a log had, the more mushrooms it grew.

So he tried something. He cut logs on purpose. Then he beat on them with his axe. And more caps popped up, thick as fish scales, or so the old telling goes.

That mushroom was the shiitake. By 1209, his method was written down in the records of Longquan County, the first written account of growing it anywhere. From there it crossed the sea to Japan, which gave it the name we use today.

People in those hills still honor him. A small temple to Wu Sangong sits by a mountain stream, and a mushroom festival fills it each fall. Log growers still soak their logs in cold water, and some still knock them, to wake them up.

Wake them up. Keep that picture in mind, because a team in Florida found something that looks a lot like it...

In the fall of 2011, a team at the University of Florida, led by the food scientist Sue Percival, handed 52 healthy adults a four-week supply of dried shiitake. People took them home, cooked them, and ate one serving a day. That's about four ounces, or one good bowl of the soup above.

The team drew blood before and after. Then they grew the cells in a lab dish and watched what they did.

What changed in four weeks: One kind of guard cell multiplied about 60% more after the mushroom month than before it. Saliva carried more of the antibody that coats your mouth and gut. And a blood marker of inflammation went down. (University of Florida, Journal of the American College of Nutrition, 2015)

Let me explain what those guard cells are.

Scientists call them gamma delta T cells. Think of them as the guards posted at the doors. They live in the lining of your gut and your skin, the places where the outside world meets you first. Nobody has to send them orders. When trouble shows up, they move first...

So why would a mushroom matter to them? You see, the walls of a shiitake are built from long chains of sugar that your body can't break down. Your gut lining is dotted with sensors that notice those chains as they pass. The leading idea is that this brush with the gut puts the guards on alert. That's a good guess. Nobody has proven it yet.

9 cents.

That's roughly what one serving costs at any grocery store in America.

A trial published in the European Heart Journal found it cut fatal heart events by 41 percent.

Forty. One. Percent.

Why hasn't your doctor mentioned it?

Same reason your doctor hasn't mentioned a lot of things…

There's no pharma rep walking into the clinic with samples of a 9-cent grocery store item.

I won't name it here. The name alone is useless. The dose, the timing, and what you pair it with are what makes the difference between 41% and zero.

>> All three are in this free documentary

It's also paired with something even bigger that I'll let you discover yourself. The kind of thing that explains why heart disease is still the #1 killer in this country after sixty years of "progress."

P.S. This 9-cent compound shows up about 14 minutes in.

Don't skip ahead… what comes before it is the reason it works.

Here's the thing. This study has three holes in it, and you deserve to see them.

First, nobody in it went without. One group ate a smaller serving and one ate a bigger one, and both got better numbers. With no mushroom-free group to compare, some of the change could be the season, or just the act of being studied.

Second, the people were 21 to 41. You're likely older, and the body's defenses tend to slow with age. Nobody has run this test on people over 60.

Third, mushroom growers in the United States and Australia paid for the work. That doesn't make it wrong. But you should know it.

And what the team measured was cells in a dish, not colds. So I won't tell you a bowl of soup keeps you from getting sick. What I believe is simpler. A food this cheap and this good, with blood tests leaning the right way, has earned a spot in your pot this fall.

Now, back to that twenty-minute simmer.

Raw or barely cooked shiitake can cause a strange rash. Red, itchy streaks show up across the back and chest a day or so later. They look like someone took a whip to you. Doctors call it shiitake dermatitis, and Japanese doctors first wrote it up in 1977.

The cause seems to be one of the sugars in the mushroom's wall, a touchy one that heat breaks down. DermNet, a skin guide started by doctors in New Zealand, puts it at about 2 in 100 people who eat the mushroom raw or lightly cooked. It fades on its own, but it can itch for weeks.

So cook it through. Every time. And notice that the Florida group cooked their mushrooms and still got their results. Cooking costs you nothing but the rash.

Look for caps that are firm and dry, curled under at the edge, with no slime. Store them in a paper bag in the fridge, not a plastic one, and use them within a week. Don't soak fresh caps to clean them. A damp towel does the job.

Dried shiitake keep for months in a jar, and they're what the Florida team handed out. Drying deepens the flavor, which is why a few dried caps make a whole pot taste rich. Pour the soaking water in slowly and stop before the grit at the bottom.

Shiitake stems are too tough to chew. But they're full of flavor. Toss them into the simmer and fish them out before you serve, or freeze them in a bag until you have enough for a pot of broth.

Wu Sangong didn't know a thing about guard cells. He just saw that a log, knocked the right way, woke up and gave more.

You don't need an axe. A pot will do, with a pound of mushrooms and twenty minutes on a Sunday. Maybe your guards wake up a little. Or maybe you just eat the best soup of the fall. Either way, you come out ahead.

Make the pot this weekend. Eat a bowl a day. See how you feel by next Friday.