Preheat oven to 350°F. Place rack in the middle. Spray a 9x12 baking dish with a nonstick spray; OR butter the form, sprinkle with flour and shake out the excess.

Combine 5 tbsp melted or room temperature cubed butter, 1/2 cup sugar and 3/4 cup flour and pulse until crumbly and pea size or smaller in size crumbs form. Alternatively use a fork to achieve the same result. Set aside.

Combine 4 eggs, 1½ cups sugar and 1 cup melted butter, 1 tsp vanilla extract and/or 2 tsp almond extract together and mix until thoroughly combined.

Add 1 cup sour cream and stir until smooth again. Add 2 cups flour, 1 tsp baking powder, 1/2 tsp baking soda, 1/2 tsp salt and stir again with minimal amount of strokes.

Add 4 cups cut up plums and gently fold everything together. Transfer to a baking dish and sprinkle with streusel topping. Bake for 35-45 minutes or until a toothpick inserted in the middle comes out clean. Serve hot with a scoop of ice-cream or cold, sliced into squares.