Preheat the oven to 350°F and grease a 9" springform cake pan with butter.
Make the topping—in a bowl, combine the flour, sugar, and butter pieces in a bowl. Crumble the marzipan into the mixture, and use your fingers to work the butter and marzipan into the flour until all the flour is wet and the crumbles are pea-sized or smaller. Set aside.
In another bowl, toss the strawberries with the 1 tbsp of flour, and set aside.
Make the cake—whisk the flour, baking powder, and salt together in a bowl. Set aside.
Cream the sugar and butter in an electric mixer until light and fluffy. Add the marzipan and combine. Add the vanilla and the egg and combine.
Fold in half of the buttermilk and half of the flour mixture, just until combined. Then repeat with the other half of buttermilk followed by the other half of flour mixture. Take care not to over work the batter.
Spoon the batter evenly into the cake pan and smooth the top. Add the strawberries, followed by the streusel topping.
Bake until a cake tester inserted in the center comes out clean, ~40-50 minutes.