To make the masa crust:

1. Preheat your oven to 400ºF.
2. In a bowl mix together masa, salt, garlic powder, and cumin until combined. Add in the butter and pour the hot water on top.
3. Mix together until it is fully combined, making sure to hydrate all of the masa. It should be the consistency of playdough. It should be soft, but it shouldn't be so wet that it sticks to your fingers. If for any reason the dough is too wet, add in a tablespoon more of masa at a time until it has reached a soft non-stick batter.
4. Pat into a 9" pan in an even layer. Crimp the edges if desired. Dock the crust on the bottom and the edges with a fork to let the steam escape and to prevent the dough from puffing up.
5. Bake in a preheated oven for 20 minutes.

For the beef filling:

1. In oil in a large skillet over medium heat. Add onion and cook until soft, about 5 minutes.
2. Add beef and cook through, about 8 minutes.
3. Add spices, cornstarch and tomato paste and cook until toasted, about 30 seconds.
4. Deglaze the pan with beef broth and cook for 3 more minutes, or until the beef mixture is very slightly thickened.

To assemble and bake:

1. Spread the refried beans in the bottom of the baked crust, next add the cooked beef, then the salsa and finally top with the cheese.
2. Bake in the oven for 20 minutes, or until the cheese has melted. If desired you can broil the cheese at the end.

Serve hot with your favorite taco toppings!