Preheat oven to 350°F (175°C). Grease a 9-inch cake pan or line it with parchment paper.
Prepare apples: In a separate medium bowl, toss apples with lemon juice, cinnamon, and brown sugar.
Make streusel: Combine flour, brown sugar, cinnamon, and salt. Rub in the butter until you have a sandy buttery streusel.
Cake batter: In a large bowl, cream butter and sugars on medium speed. Add eggs one by one. Then, add vanilla. Add dry ingredients and milk alternately on low speed. Scrape with a rubber spatula.
Assemble: Spread batter into the prepared pan. Add apples. You can make it any design you want just make sure they are added evenly. Then, add the streusel.
Bake: 40–45 minutes or until center springs back. I start checking around 35ms since my oven runs hot.
Cool: Let the cake completely cool on a wire rack.
Powdered Sugar (Optional): In true German fashion, a light dusting of powdered sugar adds a beautiful finishing touch. Simply place a little powdered sugar into a fine sieve and gently tap it over the cooled cake. You don’t need much, just enough to create a soft, snowy layer that makes the cake look even more inviting.
Serve: Enjoy warm with ice cream or cool with coffee.