preheat oven to 375 if using home oven. For Dutch oven, either pre-warm the DO or add 5-10 min to cooking time

Grease or spray an 8-inch square baking pan or deep-dish cast iron skillet or 10" Dutch Oven
In a mixing bowl combine cornmeal, flour, baking soda, baking powder, salt and brown sugar.
In another bowl, whisk together the egg, 1/2 cup of the buttermilk, squash, and vegetable oil.
Combine the wet ingredients with the dry ingredients; mix until well blended, adding more buttermilk if needed. Batter will be thick, but easy to stir by hand.
Spread batter in the prepared baking pan.

Pat top with buttermilk

For home oven: Bake for 25-30 minutes until nicely browned.

For Dutch oven - use rule of 3, turn every 5 minutes for 20-30 minutes until top is browned