The suggestion is to use raspberry jam, but I imagine you could substitute any flavor jam of your preference. This cake has a beautiful crunchy crumb topping and along with the jam layer, it makes a pretty presentation. From Gourmet Magazine, December 2007.
Preheat oven to 400 degrees F and place rack in the center of oven.
Generously butter a 9" square or round cake pan.
In a bowl, whisk together flour, sugar, baking powder and salt.
In a large bowl whisk together butter, milk and egg; then whisk in flour mixture just till combined.
Pour batter into cake pan.
Dollop jam all over surface, then swirl into batter with spoon.
Whisk together butters, sugars, cinnamon and salt until smooth.
Stir in flour, then blend with your fingertips until incorporated.
Sprinkle crumbs in large clumps over the top of batter.
Bake cake until a wooden pick inserted in center comes out clean and side begin to pull away from pan, about 25 minutes.
Cool in pan on a rack for 5 minutes before serving.
