Step 1

Preheat the oven to 400ºF.

Step 2

In a large skillet, melt the butter over medium-high heat. Add the onion and carrots and a pinch of salt and cook, stirring until soft, about 10 minutes. Stir in the flour so that it gets evenly distributed. Add 1 1/2 cups of the milk, stirring constantly until thickened. Repeat with the remaining 1 1/2 cups milk. Stir in the chicken broth, peas, chicken, thyme, and a few turns of pepper and simmer, stirring often, until the chicken is cooked through and no longer pink, 10 to 15 minutes. Taste the mixture and adjust seasonings if desired.

Step 3

Transfer the mixture to an 11x8-inch baking dish (or other 3-quart ovenproof dish) and cover with Tater Tots. Arrange them snugly and neatly. Bake until the tots are golden brown. Begin checking for doneness at 30 minutes. Let cool slightly and serve with ketchup, if desired.