1. Preheat oven to 160°C. Place the butter and sugar in a food processor and process for 2 minutes or until pale and creamy. 
2. Add the vanilla, egg yolk and chocolate and process until combined. Add the flour and cocoa and process until combined and mixture forms a ball. 
3. Place the mixture in a bowl, cover with plastic wrap and refrigerate for 30 minutes, or until firm. 
4. Roll tablespoons of mixture into balls and place on 2 large baking trays lined with non-stick baking paper. Use your thumb to press an indent into the centre of each. 
5. Cook for 12–14 minutes or until dry and cooked. Allow to cool slightly on the trays before transferring to wire racks to cool completely. Using a spoon, divide the caramel between cookies to serve. Makes 18

TIPS:

+ These desserts will keep for up to three days in an airtight container.
+ We like to use dulce de leche when using thick caramel in desserts, which is made from cooked condensed milk. Find it at specialty grocery stores.

+ To melt the chocolate in the thumbprint cookies, place the chocolate in a small heatproof bowl and set over a saucepan of just simmering water. Stir until melted and smooth. Set aside to cool slightly for 5–10 minutes.