Whisk together masa, baking powder, and salt in a large mixing bowl. Add broth and oil and stir to combine until dough becomes soft paste. Cover bowl let dough rest for at least 15 minutes at room temperature.
In the meantime, preheat oil in a large skillet over medium high heat. Reduce heat to medium and add ground venison or beef and onions. Cook until meat is no longer pink, being sure to break up any large chunks. Add minced garlic and cook for 2 more minutes. Stir in enchilada sauce.
In a small bowl, whisk together cornstarch and water. Stir in chili powder, cumin, and broth. Add mixture to meat and stir to combine.
To assemble, spread meat in an even layer over the bottom of the crock of a slow cooker. Gently spread tamale dough over the top of the meat mixture. Cover and cook on low for 3-4 hours until dough is set.