Preheat oven to 425ºF. Butter a 9-inch cast iron skillet*
In a large bowl, sift together flour, baking powder, sugar and salt.
Work butter into flour mixture with your fingertips, until flat dime size pieces are formed.
Gently stir in cheese and ham.
Stir in buttermilk a little at a time until a shaggy dough is formed.
Turn dough out onto a lightly floured surface.
Fold dough over onto itself a few times. Form dough into a 7-inch diameter 3/4-inch thick round.
Using a 2 1/2-inch biscuit cutter, cut dough into seven biscuits. Press the scraps together and cut one more biscuit. If dough becomes warm at any point, chill in the refrigerator for 10-15 minutes, then proceed with recipe.
Transfer biscuits to prepared pan. Brush with melted butter.
Bake until biscuits are puffy and tops are golden brown, about 22-25 minutes.