2poundspitted plumsquartered (halved if using prune plums)
Prep: Line a 9x13 inch cake pan and preheat the oven to 360°F.
Make the streusel: Add 1 cup flour, ⅓ cup sugar and ¼ teaspoon ground cinnamon to a small bowl. Mix well, then cut in the butter until crumbs form. Chill.
Make the cake batter: Cream 2 sticks butter, 1 cup sugar and 3 large eggs together until light and fluffy (this takes 4-5 minutes, so be patient or your cake won't rise). Slowly beat in 1 cup greek yogurt. Evenly sprinkle 2 ½ cups flour, 1 cup ground almonds, 1.5 teaspoons baking powder, 1 teaspoon ground cinnamon and ¼ teaspoon salt over the egg mixture. Slowly mix in until a smooth batter forms - batter will be thick.
Assemble and bake the cake: Spread the batter in the prepared cake tin. Evenly place the plums on top, slightly pressing them into the batter. Scatter the streusel over the cake. Bake the cake for 35-40 minutes, until a toothpick inserted into the middle comes out fairly clean. Cool in the pan on a wire rack.