Preheat the oven to 375ºF.

Heat 1 teaspoon of olive oil in small skillet over medium heat. Add the garlic and shallots and cook until the garlic is lightly toasted and shallots are translucent, making sure the garlic doesn't burn. About 2-3 minutes. Set aside.

Melt butter in medium or large saucepan over medium heat. Add masa harina and whisk until smooth. Continue cooking, whisking, until golden brown, about 6 minutes.

Meanwhile, heat milk in saucepan until just about to boil. Add milk to butter and masa harina mixture, in three parts, whisking continuously until very smooth.

Bring to a boil. Continue cooking for about 1 minute, until it thickens. Remove from the heat and add salt and nutmeg.

In a lightly greased 9×13 casserole dish or baking pan, layer, in order, 3 to 4 layers of squash slices, garlic/shallots, béchamel, and parmesan.

Sprinkle with salt and pepper, to taste.

Bake for about 35-45 minutes, until the top is golden brown and bubbling. Turn on the broiler for 3-4 minutes, if necessary

Slice and serve.