Preheat oven to 375°F. Spray a Wilton 48 cavity Mini Muffin Tin with cooking spray and set aside.
Whisk flour, baking powder and salt in a large bowl. Make a well in the center.
In another bowl, whisk vegetable oil, milk, eggs and pour into the large bowl’s well. Stir until moistened.
Stir in ½ cup ketchup, 2 tbsp mustard and 1 cup cheddar cheese. Set aside.
In a large skillet cook ground beef and onion over medium heat until ground beef is fully cooked and onion is softened.
Add 1 cup of ground beef mixture to your batter and stir to combine.
Fill muffin tin with the batter until almost full. Bake for 15 minutes or until a toothpick inserted in the center of a muffin comes out clean. Transfer muffins to a cooling rack.
Filling
Add the rest of the ground beef mixture to a small bowl. Stir in 4 ½ tbsp ketchup, 1 tbsp mustard and dill pickles.
Remove the center of each muffin with an apple corer or paring knife. Be careful to not go too deep.
Fill each muffin with the ground beef filling using a small spoon. Place muffins back into the Wilton Mini Muffin Tin. Sprinkles with ¼ cup shredded cheese.
Place back into the 375°F preheated oven to heat up and melt the cheese for about 3 to 4 minutes. Serve hot with ketchup and mustard for extra toppings.