Preheat the oven 200 degrees C. Line and grease a 9 inch cake pan.

Make the cake batter first.

Whisk together flour, sugar, baking powder, and salt in a bowl and set aside. Beat together the butter, milk, and egg in a large bowl, then gradually mix in a flour mixture until just combined.

Pour the batter into the pan. Dollop spoonfuls of the jan all over the cake surface then swirl into batter with a fork.

Crumb topping.

Combine butter, sugar, cinnamon and salt until smooth.

Stir in the flour, then blend with your fingertips or fork until incorporated and crumb have formed.

Sprinkle the crumbs in the large clumps over top of the cake.

Bake the cake for 25 minutes.

Allow the cake to cool completely before removing from the pan.

Dust with powdered sugar