Prep the pan and oven: Heat oven to 350°F (175°C). Grease a 9-inch (23 cm) springform pan and line the base with parchment.
Season the apples: Toss sliced apples with lemon juice, sugar, and cinnamon.
Set aside to lightly macerate.
Make the streusel: In a bowl, combine flour, both sugars, cinnamon, and salt. Cut in the cold butter with your fingers or a pastry cutter until it forms clumps. Chill while you make the batter.
Mix dry ingredients: Whisk flour, baking powder, and salt together in a small bowl.
Cream butter and sugar: Beat butter and sugar until light and fluffy, about 2 minutes.
Add eggs one at a time, then vanilla.
Finish the batter: Mix in half the dry ingredients, then milk, then the rest of the dry ingredients. Stir just until smooth.
Assemble: Spread batter evenly in the pan. Fan the apple slices on top in an even layer.
Sprinkle streusel generously over the apples, pressing some into larger crumbs.
Bake: Bake 40–50 minutes, until the top is golden and a toothpick in the center comes out clean or with a few moist crumbs.
Cool and serve: Let cool in the pan 15 minutes, then release the ring. Serve warm or at room temperature with whipped cream or ice cream.