Preheat oven to 350°F and butter the bottom of a skillet, 9- or 10-inch springform pan, or baking dish.
In the bowl of a stand mixer fitted with the paddle attachment (or bowl of a food processor), beat the butter and sugar until light and fluffy; about 2-3 minutes. Add in eggs, one at a time and mix on high speed, for 30 seconds, after each addition. Add vanilla extract, lemon zest and juice; mix until just combined. With the mixer on low, add the flour, baking powder, salt, and milk. Beat until just combined (and don't overmix!).
Pour and spread batter evenly into the prepared pan or skillet, smoothing the top with a spatula.
Arrange apples on top, skin side up (so the colors can be seen) and nesting them close together into the batter (optional to group by color).
For the cinnamon-sugar glaze, mix in the sugar and cinnamon with melted butter and stir until well combined. Brush glaze on top of apples and batter.
Bake cake for 40-50 minutes, until it’s golden-brown the apples have softened, and a toothpick comes out clean.
Let cake cool in pan or skillet for 5-10 minutes and serve warm.