Peel and cut the butternut squash and sweet potatoes into 1 1/2-inch cubes and place them on a baking sheet. Add the melted butter, brown sugar, cinnamon, salt, and pepper. With clean hands, toss all the ingredients together and spread in a single layer on the baking sheet. Roast for 45 to 55 minutes, until the squash and sweet potatoes are tender and the glaze begins to caramelize. While roasting, turn the squash and sweet potatoes a few times with a spatula, to be sure it browns evenly. Taste for seasonings and serve hot.