Preheat oven to 350°F (175°C).

Draw 4 circles (3 inches each) on a large piece of parchment paper.

Place paper, marked-side down, on a lightly greased baking tray.

Whisk egg whites, sugar and vanilla until thick.

Add melted and cooled butter, whisking until well combined.

Add sifted all-purpose flour.

Working in batches, spread 1 1/4 tsp batter over each circle.

Bake for 6-7 mins, or until golden at the edges.

Working quickly, remove cookies with a spatula.

Place a message in the center of each cookie.

Fold cookie in half, enclosing message.

Press edges to seal.

Mold over the edge of a glass to form a horseshoe shape.

Hold for a few seconds, or until set.

Repeat with remaining batter.