Step 1: Prepare the Cookie Batter

1. Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper.

2. In a mixing bowl, cream the butter and sugar together until light and fluffy.

3. Add the vanilla extract and egg whites, mixing until smooth.

4. Sift in the flour and salt, folding gently until well combined. Do not overmix.

Step 2: Shape and Bake the Cookies

1. Transfer the batter to a piping bag fitted with a small round tip.

2. Pipe small, thin squares (about 1.5 inches) onto the lined baking sheet, leaving space between them.

3. Bake for 8-10 minutes, or until the edges turn a light golden brown.

4. Let the cookies cool completely on a wire rack.

Step 3: Make the Filling

For Chocolate Ganache:

1. Warm the heavy cream until hot but not boiling.

2. Pour over the melted chocolate, stirring until smooth.

For Vanilla Buttercream:

1. Beat the softened butter and powdered sugar together until fluffy.

2. Mix in the vanilla extract until smooth.

Step 4: Assemble the Sandwich Cookies

1. Spread or pipe a small amount of filling onto the flat side of one cookie.

2. Gently press another cookie on top to form a sandwich.

3. Let set at room temperature, or refrigerate for a firmer texture.

Step 5: Serve and Enjoy!

• Serve with tea, coffee, or as an elegant dessert.

• Store in an airtight container at room temperature for up to 3 days, or refrigerate for up to a week.