Preheat the oven to 400 degrees F (200 degrees C). Line a large baking dish with aluminum foil.

Generously spread 2 tablespoons softened butter over squash flesh; place on the prepared baking dish, cut-sides down.

Bake in the preheated oven for 30 minutes; flip. Add 1 tablespoon cold butter and 2 tablespoons brown sugar to each squash cavity. Continue baking until outer squash shells are soft, about 10 minutes more. Spoon squash flesh into a bowl; serve.