Preheat the oven to 200 degrees C. Coat two 12 cup muffin tins with nonstick cooking spray or line with paper liners.
In a large bowl stir together the polenta, flour, sugar, baking powder, salt, chilli powder, cumin and garlic powder. Make a well in the center and pour in the milk, egg and oil. Stir until well blended, then gently stir in the cheese.
Drop a small spoonful of the batter into the bottom of each muffin cup. Place a piece of frankfurt on top of this batter. Fill cups with enough additional batter to cover the frankfurt pieces.
Bake for 10 to 12 minutes in the preheated oven or until muffins are lightly browned and spring back when lightly pressed. Cool slightly before removing from the muffin pans. Serve warm with the dipping sauce.
To make the dipping sauce whisk together the sour cream, mayonnaise and taco seasoning mix until smooth. Serve immediately.