Preheat the oven to 350 degrees F. Line a muffin tin with liners.
In a large bowl, whisk together the flour, cornmeal, sugar, baking powder and salt.
In a smaller bowl or measuring cup, whisk together the milk and eggs. Add the wet ingredients to the dry, then stir in the melted butter. Stir until just combined.
Fill the muffin liners with the batter about ¾ of the way full. Top each with a tablespoon or so of the crumble, gently pressing it into the batter.
Bake the muffins for 18 to 20 minutes, or until they are set on top. Let them cool before serving!
Note: you can make these a day ahead of time