Toss the sliced peaches with 2 tablespoons granulated sugar and 1 tablespoon lemon juice and let sit 10 minutes while you preheat the oven to 375°F; arrange peaches on a rimmed baking sheet in a single layer.

Roast the peaches 10–12 minutes until they release juice and the edges begin to caramelize; remove and cool slightly, then reduce oven temperature to 350°F.

Grease a 9-inch springform pan and line the bottom with parchment. Cream 10 tablespoons softened unsalted butter with 1 cup granulated sugar until light, then add the eggs one at a time, mixing after each, and stir in 1 teaspoon vanilla.

Whisk 1 3/4 cups flour with 1 1/2 teaspoons baking powder and 1/2 teaspoon salt; combine 1/2 cup sour cream with 1/4 cup milk. Add the dry mixture to the butter mixture in two additions alternating with the sour cream mixture, beginning and ending with dry ingredients, mixing just until combined.

Spread the batter into the prepared pan, arrange roasted peaches on top in a single layer pressing lightly, and bake at 350°F for 35–42 minutes until a toothpick inserted into the center (avoiding direct peach) comes out with moist crumbs. Cool in pan 15 minutes, then release and cool completely on a wire rack.

Beat 4 ounces room-temperature cream cheese with 1/3 cup powdered sugar and 1/2 teaspoon vanilla until smooth. Whip 1 cup cold heavy cream to soft peaks and fold into the cream cheese mixture until light. Spread over the fully cooled cake, garnish with roasted peach slices, and chill at least 30 minutes before slicing.