Combine flour, sugar, brown sugar, and cinnamon in a small bowl.
Melt the 4 Tablespoons of butter in the microwave (or on the stove top). Add the melted butter to the flour mixture and use a whisk to blend together. Set aside until ready to top cupcakes.
Preheat the oven to 350°F. Place the unbroken eggs in a bowl of warm water to bring them to room temperature, set aside
Peel and dice the apples, toss with lemon juice in a small bowl and set aside.
Sift the flour, baking powder, and cinnamon into a mixing bowl. Add the salt and whisk well to combine, set aside.
In the bowl of a stand mixer, fitted with the flat beater, beat the softened butter on medium speed for 1-2 minutes. Scrape down the sides of the bowl.
Add the sugar and vanilla to the butter and mix on low until incorporated, then beat on medium speed for 2-3 minutes until the butter is light a fluffy. Scrape down the sides of the bowl.
Add the eggs one at a time, mixing on low speed after each addition until well incorporated. Be sure to scrape the bowl in between additions.
Add the flour mixture to your mixing bowl in 3-4 batches alternating first with the applesauce and then with the milk. Scrape down the sides of the bowl and mix well (about 30-40 seconds) after each addition.
Drain any juices from the diced apples, toss with a little extra flour to coat, then fold into the batter.
Fill each cupcake liner with about 1/4 cup of batter. I like to use a #16 disher/scoop to portion out my cupcake batter (see recipe notes).
Top each cupcake evenly with streusel topping then bake @ 350°F for about 20 minutes or until a wooden toothpick comes out clean. Let the cupcakes cool in the pan for 10 minutes, then remove onto a cooling rack.
Best served warm and topped with whipped cream and caramel sauce (see recipe notes).