Crock pot potato soup: hold the dairy until the end

For a 6-quart crock pot, cook 3 pounds of cubed russet potatoes, a diced onion and 4 cups of chicken stock on LOW for 7 to 8 hours or HIGH for about 4, until a cube crushes against the side with a spoon. Then mash about half the potatoes in the pot, stir in 1 cup of heavy cream and 4 ounces of cream cheese, and cook 30 minutes more on LOW. The cheddar goes in last, with the cooker on WARM.

Most recipes have you dump everything in at 7 a.m., milk included. By dinner the soup has a fine grain to it, there's a tan ring at the waterline, and the cheese floats in oily threads.

The dairy goes in last.

Why does the dairy go in last?

A slow cooker isn't as gentle as it sounds. Both settings eventually bring the contents close to a simmer, and LOW just takes longer to get there. Eight hours near a simmer is long enough for milk proteins to tighten into small curds, and the lactose and potato starch along the hot crock wall slowly brown into that ring.

I ran it side by side: two 6-quart cookers, same potatoes and stock, one with 2 cups of whole milk added at the start and one with the milk added for the last 30 minutes. After 8 hours on LOW, the early-milk batch was flecked with tiny curds and had a brown crust at the waterline. The late batch was smooth.

On a restaurant line, cream soups get their dairy at the end, and often per order, because a base can hold all day but cream can't. You don't need to finish by the bowl at home. The last 30 minutes in the crock is close enough.

Related: Why Is My Broccoli Cheddar Soup Grainy?

How to make it, step by step

Russets break down and thicken the soup on their own. Yukon Golds hold their cubes and taste more buttery but give a thinner body, so use them if you like a chunky soup and plan to mash a little more. Waxy red or new potatoes barely thicken at all.

1. Cut the potatoes evenly. Peel 3 pounds of russets (about 6 medium) and cut them into 3/4-inch cubes. Mixed sizes give you mush and hard bits in the same spoonful.
2. Sweat the onion first if you have 10 minutes. Cook 1 diced medium onion and 2 minced garlic cloves in 2 tablespoons of butter over medium heat for about 8 minutes, until soft and translucent. Raw onion in a slow cooker steams and tastes flat. Skipping this still works. The soup is just less round.
3. Use less liquid than you think. Add 4 cups of stock, which should sit just below the top of the potatoes. The lid traps nearly all the steam, so nothing reduces. Add 1 teaspoon of kosher salt, 2 thyme sprigs and a bay leaf, and keep the crock no more than two-thirds full.
4. Cook until the potatoes crush. Give it 7 to 8 hours on LOW or 3 1/2 to 4 hours on HIGH. Pull three cubes from the center, not the edge, and press each against the crock with a spoon. All three should collapse with no resistance.
5. Mash half in the pot. Fish out the thyme and bay. Use a potato masher for 10 to 12 strokes, or an immersion blender for three or four short pulses. Blending the whole pot smooth for a minute or more works the starch and turns russets gluey.
6. Add the cream and give it 30 minutes. Stir in 1 cup of heavy cream or half-and-half and 4 ounces of softened cream cheese in small cubes. Cover and cook on LOW for 30 minutes, stirring once halfway.
7. Melt the cheese on WARM. Switch to WARM and stir in 6 ounces (about 1 1/2 cups) of sharp cheddar grated from a block, a handful at a time. Taste for salt only now, since cheese and bacon both add plenty. Top with bacon cooked on the stove and sliced chives.

When to change the plan

If the soup is thin, mash more potatoes, or cook it uncovered on HIGH for 30 minutes. If it's too thick, add stock 1/2 cup at a time. Whole milk can replace the cream, but it curdles more easily, so add it in the last 15 minutes. Skim milk will break, so leave it out.

If you want it thicker without more mashing, a light roux whisked into the cream before it goes in will do it. Two tablespoons each of butter and flour is enough for this batch.

On leftovers, the USDA says to refrigerate within 2 hours, eat them within 3 to 4 days, and reheat to 165°F on the stove or in the microwave rather than in the slow cooker, which heats too slowly. The finished soup freezes badly. The potatoes turn grainy and the dairy separates on thawing.

Related: Slow Cooker vs Instant Pot: Which One Wins?

I freeze half the base before the cream goes in and finish the rest that night. The frozen half gets its cream and cheese the day I reheat it.