Preheat oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan. Prepare the rhubarb filling by tossing the chopped rhubarb, 1/4 cup sugar, and cornstarch together in a small bowl. Set aside.

Prepare the streusel topping: In a medium bowl, combine flour, brown sugar, slivered almonds, cinnamon, and salt. Cut in the cold butter using a pastry blender or your fingers until the mixture resembles coarse crumbs. Cover and chill until needed.

Prepare the cake batter: In a large bowl, whisk together the flour, baking powder, and salt. In a separate bowl, cream together the softened butter and 1 cup sugar until light and fluffy. Beat in eggs one at a time, then mix in vanilla and almond extracts.

Alternate adding the dry ingredients and the sour cream to the wet ingredients, beginning and ending with the dry mixture. Mix until just combined, being careful not to overmix.

Spread half of the cake batter evenly into the prepared baking pan. Sprinkle the rhubarb mixture evenly over the batter. Top with the remaining cake batter, gently spreading it over the rhubarb layer.

Sprinkle the chilled almond streusel topping evenly over the top of the cake batter. Bake for 45 to 50 minutes, or until a toothpick inserted into the center comes out clean.

Let the cake cool in the pan on a wire rack for at least 20 minutes before slicing and serving warm or at room temperature.