In a medium bowl, combine all-purpose flour, light brown sugar, and a pinch of salt. Mix in cold unsalted butter until the mixture resembles coarse crumbs. Fold in chopped hazelnuts and refrigerate.

Set your oven to 350°F (175°C) and grease a 9”x 13”x 2” baking pan. Preheating ensures even baking.

In a mixing bowl, beat together cream cheese, granulated sugar, additional flour, egg, and vanilla extract until smooth. Set aside.

In another bowl, whisk together the remaining flour, cocoa powder, baking powder, baking soda, and a pinch of salt.

Cream together softened unsalted butter, granulated sugar, and light brown sugar until light and fluffy. Add eggs one at a time, incorporating fully.

Gradually add the dry ingredients to the butter mixture, alternating with yogurt until just combined. Avoid overmixing.

Spread the prepared cake batter evenly in the greased baking pan.

Drop spoonfuls of the cream cheese mixture over the cake batter and gently swirl.

Sprinkle the hazelnut crumb topping evenly over the cake.

Bake for 40 to 45 minutes until a toothpick comes out clean. The top should be golden brown.

Let it cool in the pan for 10-15 minutes before serving.