Toss the sliced plums with the lemon juice and set aside in a fine mesh colander to drain. Preheat an oven to 350 F and place the rack in the center of the oven. Grease a 10" tube pan or 10 cup bundt pan with a baking spray that contains flour.
In a stand mixer, cream together the butter and sugar until fluffy. Add the eggs one at a time, mixing well after each addition. Add the sour cream and vanilla and mix until just incorporated, scraping the sides and bottom of the bowl, mixing more as necessary.
Whisk cake flour, baking powder, baking soda and salt in a smaller separate bowl. With the mixer running on low speed, slowly add the flour mixture to the wet ingredients, stirring on low speed until just incorporated. Using a rubber spatula, scrape the sides and bottom of the bowl and stir by hand to incorporate any wet or dry spots.
Pour half of the batter into the prepared cake pan. Top with half of the crumb mixture, followed by an even layer of plums. Top the plums with the remaining crumb mixture before pouring in the remaining batter, making sure to leave at least 1" of space between the batter and the top of the pan. Smooth the batter with a rubber spatula and place on a large rimmed baking sheet and into the oven.
Bake at 350 F for 50-60 minutes, or until the top of the cake is an even shade of golden brown and is completely set. Cool completely on a wire rack before carefully flipping out of the pan.
Whisk the milk and powdered sugar to form the glaze. Drizzle onto the cooled cake with a tablespoon. Slice and serve!