In a food processor, pulse together your flour, baking powder, and salt. Add your butter and pulse 3-4 times. You'll want your butter to be the size of peas and just incorporated into the flour. Pour the mixture in a large mixing bowl. Make a well in the center, and pour the buttermilk in, folding it into the flour with a rubber spatula. 

Once the biscuit batter just begins to form into one mass, flip it onto a heavily floured work surface. Begin to fold it until it comes together. With a rolling pin, rolls it into a 2" thick rectangle. Spread half the cheddar, ham, and scallions on top. Fold the dough in half, and then roll it out to another 2" rectangle. Spread the remaining cheddar, ham, and scallions. Fold the dough in half, and then roll it out to another 2" rectangle. Using a biscuit cutter (see note), cut your biscuits and lay them on a baking sheet lined with a silpat baking mat or parchment paper. Put the tray of biscuits into the freezer and freeze for 30 minutes.

Preheat the oven to 425°F. Take the biscuits out of the freezer and place them directly into the oven. Bake for 30 minutes, or until they just begin to turn golden on top.