Steps
1. Preheat oven to 180°C (350°F) and grease a small ramekin with butter, then dust with cocoa powder.
2. In a bowl, whisk the egg and sugar until fluffy.
3. Sift together flour, cocoa powder, and cinnamon; gently fold into the egg mixture.
4. Stir in the melted butter and half of the chopped hazelnuts.
5. Pour half of the batter into the prepared ramekin.
6. Arrange a few thin apple slices and sprinkle some chocolate chips and remaining hazelnuts on top.
7. Cover with the rest of the batter.
8. Bake for 15-18 minutes or until a toothpick comes out mostly clean.
9. Let cool slightly before unmolding. Serve warm for a gooey texture.