Grilled Cheese Pancakes
In a large bowl, whisk together flour, baking powder, salt, and sugar. In a medium bowl, whisk to combine milk, sour cream, egg, and melted butter. Gently fold dry ingredients into wet ingredients until just combined.
In a large skillet over medium heat, melt ½ tablespoon butter. Pour a scant ⅓ cup pancake batter into pan twice to make two pancakes. When little bubbles appear, about 3 to 4 minutes, flip one pancake and top with ¼ cup cheddar, ¼ cup mozzarella, 1 tablespoon Parmesan, and a pinch black pepper. Flip remaining pancake. Continue cooking until second side is golden and cheese is melty, 3 minutes more.
Top cheesy pancake with plain pancake, then evenly spread ½ tablespoon mayonnaise onto the top pancake. Flip and cook until a golden crust forms, 1 minute. Spread ½ tablespoon mayonnaise on to the second side, then flip to cook until a golden crust forms, 1 minute more. Transfer sandwich to a plate.
Repeat with remaining batter, cheeses, and mayonnaise.
Serve with maple syrup and garnish with bacon, if desired.