Preheat the oven to 400 degrees. Pulse the flour, baking powder, salt and baking soda in a food processor until combined. Add the butter and pulse until the mixture looks like coarse meal. Pulse in the buttermilk, cheese and dehydrated onion until incorporated.
Roll out the dough to 1/2 inch thickness on a lightly floured surface, then fold in half and refill. Cut out 2-inch rounds with a biscuit cutter. Arrange on a baking sheet and bake until golden, about 15 minutes.
Split the biscuits in half. Add peach jam and/or mustard and ham.
You can switch up the kinds of mustard to vary this sandwich. Try fig jam, horseradish mustard, Dijon mustard, raspberry preserves or any others of your choice.
You can make these small for appetizers or make them slightly large for lunch or dinner.