In a bowl of a stand mixer, or large bowl if using a hand mixer, combine the flour, brown sugar, cinnamon, baking powder and baking soda and salt. Turn mixer on low and mix until just combined.
Add in the butter one tablespoon at a time and mix on low until well combined. It will resemble wet sand.
Slowly add in the egg mixture and beat on low, stopping to scrape down the sides of the bowl. Once all is combined, raise speed to medium and mix for another 30 seconds. Scrape down the bowl again to make sure it is well mixed.
Pour two-thirds of the batter into the bundt pan, making sure it is spread evenly. Add in either one-third to half the streusel, then the apples and then the remaining third or rest of the streusel. If filling with all the streusel add the with remaining batter and carefully spread it so no streusel is showing. If adding streusel to the top, fill the top with the remaining batter then sprinkle the rest of the streusel over the top.
Bake for 70 minutes or until a toothpick comes out clean. If the top is starting to brown too much and the middle isn’t done yet cover with a piece of foil until done.
Let cool in the pan for 10 min then flip onto a wire cooling rack a cake plate or serving platter and carefully remove bundt pan. Let cool completely before icing. Around 4 hours. You can wrap the cake in plastic wrap and store at room temperature overnight before icing.