Preheat oven to 375°. Heat oil in a large frying pan over medium-low heat. Add onion and cook until soft, 3 to 5 minutes. Add garlic and pork and cook, breaking meat up in pan, until pork is browned and slightly crisp, 5 to 8 minutes more. Stir in cumin, tomato paste, chipotle chile, 1/2 cup water, salt, and pepper and cook until liquid has evaporated, about 3 minutes. Remove from heat.
Meanwhile, mix masa harina with 1 1/2 cups water until smooth, using your hands if needed. Using a mixer with the whisk attachment, whip lard first on low speed, then on high, until very fluffy, about 5 minutes. With mixer on low, gradually add masa harina in a few additions, beating well after each one and scraping down sides of bowl as needed. Gradually add chicken stock and baking powder, mixing well on medium speed until dough is very smooth and pliable.
Spray 2 muffin pans with cooking spray. With wet hands, press about 3 tbsp. masa dough into each muffin cup to line it and form a well. Fill each cup with pork mixture, then bake until golden brown, 25 to 30 minutes. Let cool about 5 minutes, then remove from pan. Top with cheese, a squeeze of lime, some hot sauce, and cilantro.
*Masa harina is fresh corn dough that's been dried and ground into flour. Find it in the international aisle of your grocery store or at Latino markets. For the best flavor and lightest texture, get fresh lard (rather than shelf-stable hydrogenated lard) from a butcher shop or a Latino market.
Note: Nutritional analysis is per tamale bite.