Finely dice 2 Frigo® Cheese Heads® String Cheese sticks and slice the remaining 2 into 1/8-inch thick coins. Set aside.
In a large bowl, combine the flour, baking powder, baking soda, sugar and salt. Mix well and set aside. Then, add the butter and cut in with a pastry cutter until the mixture is about the size of peas and very crumbly. Stir in the diced cheese sticks and pepperoni. Then, stir in the buttermilk only until the dough holds together, about 30 seconds.
Turn the dough out onto a floured board, kneading it 3–4 times. Pat it into a 9-inch x 5-inch rectangle and sprinkle it with additional flour. Then, fold it into thirds and repeat, beginning with pressing it into a rectangle again, sprinkling it with flour and folding it into thirds. Repeat one more time.
Then, press the dough out to a 1/2-inch thickness. Dip a heart-shaped 2 1/2-inch cutter in flour and cut the biscuits. Transfer them to a parchment-lined baking sheet, placing the biscuits side-by-side so they touch. And continue with the remaining dough, pressing together again.
Bake for 10 minutes or until the biscuits begin to brown. Then, brush the tops of the biscuits lightly with the marinara and top with the remaining cheese coins. Bake 3–4 minutes more until lightly browned and the cheese coins are soft. Finally, slide the parchment paper onto a cooling rack and cool 2 minutes before serving.