preheat the oven to 450°
peel and dice the potatoes
meanwhile heat the oil in the frying pan over medium high heat
add the potatoes and onions to the oil and salt them
quickly cook until the potatoes are just soft
sprinkle with the paprika and flour
cook and stir for 2-3 minutes
add the water to the pan and deglaze the pan, it will steam up a bit but keep scraping the bottom of the pan until it's clean
sprinkle in the au jus powder and stir to combine
pour in the frozen vegetables and the roast beef
bring the filling to a boil and then reduce it to a simmer, and let it cook down while you make the biscuit topping
make the biscuit topping, mix the flour, baking powder, cream of tartar, salt and sugar together, set aside
cut the cold butter into pieces and toss it with the dry ingredients
use your hands or a pastry blender to rub or cut the butter into the flour mix until it resembles crumbs
add the milk and stir until the dough comes together
lightly flour the counter and lay the dough out
knead it lightly 6-8 times
pat into a circle
turn the heat off under the beef mixture
lay the crust over the filling don't worry about the crust going all the way to the edge, just get it close
cut a few vent holes in the top
bake the pot pie in the preheated oven for 14-16 minutes
serve bubbling hot