Butter an 8 x 8 baking pan.
Preheat oven to 375 degrees Fahrenheit.
Melt butter in the microwave in a large mixing bowl.
Stir in sugar and eggs. Mix until well blended.
Mix in gluten-free flour mix, cornbread and salt. Stir until blended.
Pour mixture into prepared baking pan.
Bake in preheated oven for 35-40 minutes. Toothpick inserted in the middle should come out clean.