Preheat oven to 425°F. Mist two mini muffin pans (12 cups each) with nonstick cooking spray. Melt butter in small saucepan over mediumlow heat. Add onion and cook, stirring, for 3 minutes (do not let brown). Add garlic and cook for 2 minutes longer, stirring often. Set aside to cool.
Whisk together flour, cornmeal, sugar, baking powder, salt, baking soda and cayenne pepper. In a separate bowl, whisk together yogurt, milk and eggs. Stir in onion mixture and cheese. Make a well in flour mixture and add milk mixture, stirring until just combined (do not overmix).
Spoon 1 Tbsp. of batter into each muffin cup. Bake 10 to 12 minutes, until a toothpick dipped in center of a muffin comes out clean. Place pans on a wire rack to cool for 5 minutes. Remove muffins to rack to cool slightly. Serve warm.