2 tablespoons unsalted butter, melted and cooled slightly, plus 1 tablespoon for griddle
Preheat griddle to 375 degrees, or heat griddle pan over medium-high heat. Whisk flour, sugar, baking powder, and salt in medium bowl. Add egg, milk, and 2 tablespoons melted butter; whisk to combine. Batter should have small to medium lumps.
Preheat oven to 175 degrees. Test griddle by sprinkling with a few drops of water. If water bounces and spatters, it is hot enough. With paper towel, brush 1/2 teaspoon butter onto griddle. Wipe off excess.
Fill a pastry bag fitted with a 1/4-inch plain round tip with batter; twist end of bag, and secure with rubber band. Working in batches, pipe heart shapes, drawing V of batter in center of hearts to fill, on heated griddle. When pancakes have bubbles on top and are slightly dry around the edges, about 2 minutes, flip over. Cook until golden on the bottom, about 1 minute.
Repeat with remaining batter, using 1/2 teaspoon butter on griddle for each batch, keeping finished pancakes on a heat-proof plate in the oven until ready to serve.