Step 1: Preheat your oven to 375°F (190°C). Grease and flour a 9-inch springform pan, and line the bottom with parchment paper for easy removal. This ensures a smooth release of your delicious plum recipe cake.
Step 2: Prepare the Crumble Topping: In a medium bowl, combine 1 cup all-purpose flour, 1/2 cup granulated sugar, 1/2 teaspoon ground cinnamon, and a pinch of salt. Cut in the 1/2 cup of cold unsalted butter, diced, using your fingertips or a pastry blender, until the mixture resembles coarse crumbs. Place the bowl in the refrigerator while you prepare the rest of the cake.
Step 3: Prepare the Plums: Wash, pit, and slice approximately 1.5 lbs of fresh plums into 1/2 to 3/4-inch wedges. In a bowl, gently toss the plum slices with 1 tablespoon of granulated sugar and 1 teaspoon of fresh lemon juice. Set aside.
Step 4: Make the Cake Batter: In a large mixing bowl, cream together the 1/2 cup softened unsalted butter and 1 cup granulated sugar with an electric mixer until the mixture is light and fluffy. Beat in the 2 large eggs, one at a time, mixing well after each addition. Stir in 1 teaspoon vanilla extract.
Step 5: Combine Dry and Wet Ingredients: In a separate medium bowl, whisk together 1.5 cups all-purpose flour, 1.5 teaspoons baking powder, and 1/4 teaspoon salt. Gradually add the dry ingredients to the wet ingredients, alternating with 1/2 cup milk. Begin and end with the dry ingredients. Mix until just combined; be careful not to overmix the batter.
Step 6: Assemble the Cake: Pour the cake batter into the prepared springform pan, spreading it evenly to form the base of your plum recipes masterpiece. Arrange the sugared plum slices over the batter in a single layer, pressing them gently into the batter. Evenly sprinkle the chilled crumble topping over the plums.
Step 7: Bake: Transfer the pan to the preheated oven and bake for 45-50 minutes, or until a wooden skewer or toothpick inserted into the cake part (avoiding a plum) comes out clean, and the crumble topping is beautifully golden brown. If the crumble begins to brown too quickly, you can loosely tent the cake with aluminum foil.
Step 8: Cool and Serve: Let the cake cool in the pan on a wire rack for at least 20 minutes before carefully removing the springform ring. Allow it to cool further before slicing and serving. This allows the cake to set and makes for cleaner slices. Enjoy your homemade plum recipes!