Preheat oven to 400° F/204 C°.
Spoon a bit (a tablespoon or less) of the melted butter into the bottom of a 9-inch pie plate, cake pan or cast-iron skillet and grease the dish.
Whisk flour, cornmeal, light brown sugar, kosher salt, and baking powder together in a medium bowl.
Whisk eggs, mayonnaise or sour cream and buttermilk together in a medium bowl.
Whisk wet ingredients into the bowl with the dry, but just until combined.
Add the remaining melted butter to the cornbread batter and gently fold until it’s totally incorporated.
Pour the batter into the prepared pan, smooth the top and bake until the edges are deeply browned and crispy and the top is a lovely, sunflower-y golden yellow color.
Remove from oven and let cool before slicing.
