Prepare pan: Grease 10-inch Bundt pan very well with butter or spray. Dust with flour, tap out excess.
Preheat oven: Heat to 325°F. Position rack in center of oven.
Mix dry ingredients: Whisk flour, baking powder, baking soda, and salt in medium bowl. Set aside.
Cream butter and sugar: Beat butter and sugar on medium speed 3-4 minutes until light and fluffy.
Add eggs: Add eggs one at a time, beating well after each. Scrape bowl between additions.
Add lemon and vanilla: Mix in lemon juice, lemon zest, and vanilla on low speed until combined. Batter may look slightly curdled—this is normal.
Combine wet ingredients: Whisk sour cream and milk together in small bowl.
Alternate ingredients: Add flour mixture in three parts, alternating with sour cream mixture in two parts. Start and end with flour. Mix on low just until combined after each addition.
Final mix: Gently stir with spatula, scraping bottom and sides to ensure everything is mixed.
Pour and bake: Pour into prepared pan. Tap on counter 2-3 times to release air bubbles. Bake 50-60 minutes until toothpick comes out clean.
Make glaze: While cake bakes, whisk powdered sugar, lemon juice, melted butter, and lemon zest until smooth.
Cool slightly: Let cake cool in pan 10 minutes on wire rack.
Invert cake: Place wire rack over pan. Using oven mitts, flip together. Lift pan away slowly.
Glaze warm cake: Poke holes all over warm cake with toothpick. Pour half the glaze over, wait 5 minutes, pour remaining glaze.
Cool completely: Let glazed cake cool completely on rack. Glaze will soak in and set.
Serve: Transfer to serving plate. Garnish with lemon zest, berries, or whipped cream if desired.