Preheat the oven to 375F (190C) and grease a 9-inch cast-iron skillet or baking dish.

In a large mixing bowl, whisk together the cornmeal, all-purpose flour, granulated sugar, baking powder, baking soda, and salt.

In a separate bowl, combine the sourdough discard, whole milk, melted unsalted butter, honey, and eggs until smooth.

Pour the wet ingredients into the dry ingredients and stir gently until just combined; do not overmix.

Transfer the batter to the prepared skillet and smooth the top with a spatula.

Bake for 25 to 30 minutes, or until a toothpick inserted into the center comes out clean and the edges are golden brown.

Remove from the oven and immediately rub the top with salted butter until melted and glossy. Cool slightly before slicing.