Preheat your oven to 350°F and lightly grease a 7x5-inch baking dish. If you’d like to be able to lift the cake out of the dish, line with a sheet of parchment paper.
In a small bowl, stir together apples, sugar, lemon juice and cinnamon. Set aside.
In a small bowl, combine softened butter, brown sugar, flour, and cinnamon. Use a fork to mix ingredients until the mixture resembles a thick paste. Set aside.
In a small bowl, whisk together flour, baking powder, and salt.
In a medium bowl, combine softened butter and sugar and beat until light and fluffy. Beat in room temperature egg and vanilla until well-combined. Add sour cream and one tablespoon of the milk. Beat until smooth,
Add half of the flour mixture and mix until just combined. Repeat with remaining tablespoon of milk and second half of the flour mixture.
Transfer batter to your prepared baking dish, smoothing out the top.
Combine apple and butter and sugar mixture and stir together. Drop spoonfuls of the mixture over the top of your cake until it is all gone. Use a knife to swirl mixture into the batter. Cut deeply into the batter when swirling. You don’t want to completely mix the apples into the batter, but you should see some batter at the top.
Bake for 27 to 35 minutes, until a toothpick inserted into a cakey section near the center comes out with just a few moist crumbs.
While your cake is still warm, in a small bowl, combine all glaze ingredients. Whisk until smooth and pour over the cake. Allow the glaze to set for 15 to 20 minutes.
Serve and enjoy!