Step 1: Preheat your oven to 400°F. Cut a medium butternut squash in half, remove seeds, and place cut-side down on a baking sheet. Roast for 45-50 minutes until very tender. Cool, scoop out the flesh, and mash until smooth to create the puree for your roasted butternut squash and brown sugar cake.
Step 2: Lower the oven temperature to 350°F. Grease and flour a 9×13 inch baking pan or a large bundt pan.
Step 3: In a large bowl, cream together the softened butter and dark brown sugar until light and fluffy, about 5 minutes.
Step 4: Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract and the 2 cups of roasted butternut squash puree.
Step 5: In a separate bowl, whisk together the flour, cinnamon, nutmeg, ginger, baking powder, baking soda, and salt.
Step 6: Gradually add the dry ingredients to the wet ingredients, mixing on low speed or folding by hand until just combined. Do not overmix the roasted butternut squash and brown sugar cake batter.
Step 7: Pour the batter into the prepared pan and smooth the top. Bake for 45-55 minutes, or until a toothpick inserted into the center comes out clean.
Step 8: Allow the roasted butternut squash and brown sugar cake to cool in the pan for 15 minutes before transferring to a wire rack to cool completely.