Butternut squash is a hard-skinned winter squash with dense, sweet, orange-colored flesh. Its outer shell is thin and easy to peel. Butternut squash is especially rich in vitamin A, and also a good source of vitamins C and E. It's a beneficial source for the minerals magnesium, potassium, iron and calcium, as well as dietary fiber. Butternut squash may be roasted, braised or even grilled.