Ingredients
Equipment
Method
Make the dough
- Preheat the oven to 350°F.
- Line two 18x13-inch rimmed baking sheets with parchment paper.
- Beat the butter and sugar in a large bowl until light and fluffy, about 2 minutes.
- Beat in the egg yolk and vanilla.
- Whisk the flour, cocoa powder, and salt in a medium bowl.
- Add the flour mixture to the butter mixture and mix just until a soft dough forms.
- Cover and chill the dough for 30 minutes.
Shape and bake
- Beat the egg white with a fork until foamy.
- Roll the dough into 24 balls, about 1 tablespoon each.
- Dip each ball in the egg white.
- Roll each ball in the chopped hazelnuts.
- Arrange the balls about 2 inches apart on the prepared sheets.
- Press a deep indentation into each ball with your thumb.
- Bake both sheets for 11–13 minutes, switching and rotating the pans halfway through, until the cookies are set at the edges.
- Press the indentations again while the cookies are warm.
- Let the cookies cool on the sheets for 5 minutes.
- Transfer the cookies to a wire rack to cool completely.
Fill the cookies
- Spoon about 1 teaspoon of chocolate hazelnut spread into each cookie indentation.
Notes
For neat centers, press the indentations again while the cookies are warm. Store in an airtight container in the refrigerator for up to 5 days; freeze for up to 2 months. For a gluten-free variation, use a 1:1 gluten-free baking flour blend.