Step 1. Preheat oven to 350°F (175°C). Generously butter and flour a 10–12 cup bundt pan (or spray with nonstick baking spray).

Step 2. In a medium bowl, whisk together flour, baking powder, and salt. Set aside.

Step 3. In a large bowl, cream together the butter and sugar with an electric mixer on medium speed until light and fluffy, about 2–3 minutes.

Step 4. Beat in the eggs one at a time, mixing well after each addition.

Step 5. Add the sour cream and vanilla; mix until smooth. Batter may look slightly curdled — that’s fine.

Step 6. On low speed, mix in the dry ingredients in two additions, just until combined. Do not overmix.

Step 7. Toss the chopped plums with a spoonful of flour to coat (and blot with paper towels if very juicy). Gently fold them into the batter.

Step 8. Spoon the batter evenly into the prepared pan and smooth the top. Tap the pan gently on the counter to release air bubbles.

Step 9. Bake for 45–55 minutes, or until a toothpick inserted into the center comes out clean (test in a few spots, not just a plum pocket). Tent loosely with foil if browning too quickly.

Step 10. Cool the cake in the pan for 12–15 minutes, then carefully invert onto a wire rack. Let cool completely.

Step 11. (Optional Glaze) Whisk together powdered sugar, milk, and vanilla until smooth. Drizzle over the cooled cake.