Preheat the oven and combine the wet ingredients - Preheat the oven to 400℉, convection bake setting. Microwave the water and butter together until the butter melts. (I use a Pyrex glass measuring cup.) Let it cool just a bit, then whisk in the egg.
Make the dough - Whisk the masa, salt, garlic powder, and cumin together in a bowl. Stir the wet ingredients into the dry ingredients, and mix until the masa is fully hydrated. It will feel like playdough. If it's even a bit sticky, add more masa, 1 T at a time, until you have a smooth consistency that's not at all sticky.
Form the crust - Pat the dough into the pie plate with your fingers, then cover with plastic wrap and using the bottom of a 1-cup measuring cup, smooth the bottom and then the sides. Crimp the edges with your fingers, using the plastic wrap to keep your crimping smooth. Take your time to make it pretty - the dough will be well-hydrated and forgiving. Using a fork, prick the crust across the bottom and around the sides to keep the crust from puffing up.
Parbake - Bake in the preheated oven for 16 minutes.