Peel, halve, and seed the acorn squash and cut them crosswise into 1/8-inch-thick slices.
Set aside.
Peel, halve, and seed the butternut squash and cut them crosswise into 1/8-inch-thick slices.
Set aside.
Peel and halve the potatoes and cut them into 1/8-inch-thick slices.
Set aside.
Core the tomatoes and cut them into 1/8-inch-thick slices.
Set aside.
Toss together all the ingredients listed under Garlic-Herb Crust and reserve.
Preheat the oven to 325 degrees.
Grease a 2- to 2 1/2-qt casserole.
Starting and ending with acorn squash, arrange the squashes, potatoes, and tomatoes in alternating layers in the casserole, lightly seasoning each layer with salt and pepper.
In a medium saucepan, gently simmer the chicken stock, cream, garlic, horseradish, and thyme for 5 min.
Pour over the squash.
Bake the casserole, covered, for 30 min.
Then spread the crust proportionately over the surface of the casserole.