Heat oven to 350°F. Grease a 9-inch round pan and line bottom with parchment.
Pour melted butter into the pan and tilt to coat the bottom evenly.
Sprinkle brown sugar over the butter. Toss strawberries with lemon juice and cornstarch, then spread in pan.
Whisk flour, granulated sugar, baking powder, and salt in a large bowl.
In another bowl, whisk milk, eggs, oil, vanilla, sour cream, and lemon zest until smooth.
Add wet mixture to dry ingredients. Stir gently until just combined; do not overmix.
Dollop batter over strawberries, then spread to the edges. Tap pan to release air bubbles.
Bake 38–45 minutes, until golden and a tester comes out clean from the center.
Cool 10 minutes. Run a knife around edges, invert onto a plate, and peel off parchment.
Slice and serve warm or at room temperature. Add whipped cream if you like.