In a large mixing bowl, whisk together the dry ingredients ( flour, sugar, baking powder, soda and salt ).
Add cubed butter and cut it in with a pastry cutter or fork, until coarse crumbs form.
Add grated sweet potato and stir with a wooden spoon. Add cheese and stir again.
In a small bowl, combine milk and egg. Stir well.
Add to dry ingredients. Fold in gently until everything is moistened. Flour clumps are okay. DO NOT OVER-MIX!
Transfer the dough onto a piece of parchment or freezer paper. Gently form into a disk and wrap tightly. Refrigerate at least 1 hour or preferably overnight.
When ready to bake, preheat your oven to 425 degrees Line a baking sheet with parchment paper and set aside.
Unwrap the dough. Flour a biscuit cutter and cut out as many biscuits as you can. Glue the scraps together without kneading the dough and cut out the rest of the biscuits. Transfer onto a lined baking sheet. Brush the tops with melted butter. You should have some butter leftover. Set that aside.
Bake biscuits for 15 - 18 minutes, or until the tops are golden brown.
Brush the baked biscuits with the rest of the butter right after pulling them out of the oven.
Let cool on baking sheet for 2 minutes, then transfer onto a wire rack.
For a sandwich: slice still warm biscuit in half, add a Pepper Jack cheese slice, fried egg and a tomato slice. Serve immediately.