Add sweet potato cubes into a medium pot of boiling salted water until tender, about 8-10 minutes. Drain and let potatoes cool a bit before mashing.
Pre-heat oven to 425 degrees and lightly grease a 9-inch cake pan or pie plate.
In a large bowl, mix together flour, brown sugar, baking powder, salt, baking soda, and cayenne.
Add butter to the flour mixture and toss to coat. Using a pastry blender, fork, or your fingers, blend together until mixture resembles coarse meal.
In a separate medium bowl, mix together ¾ cup of mashed sweet potato and buttermilk until mixture is smooth.
Add sweet potato mixture to bowl with flour mixture and toss together using a fork. Then, using your hands, gently knead in bowl until mixture comes together.
Place dough on a floured work surface and pat into a 1-inch thick round. Using a 1 ½-inch biscuit cutter, cut out biscuits. If you don’t have a biscuit cutter, you can use the top of a drinking glass or simply roughly shape the dough by hand. Flour biscuit cutter before each cut to avoid sticking.
Gather scraps once to cut out more biscuits. You should get about 12 biscuits.
Arrange biscuits in prepared pan and brush them with melted butter.
Bake biscuits for about 22 minutes, until they're puffed and golden on top. Let them cool for about 10 minutes before removing from pan and slicing in half.
Spread mustard on a biscuit half and layer with ham and cheese (if desired). I like to cut pieces of ham and cheese with my biscuit cutter so they fit perfectly on the biscuits. Top with second biscuit to make a sandwich and drizzle with a little bit of honey.