Instructions:

• Preheat your oven to 350°F (175°C). This ensures your cake bakes evenly.
• Grease a 9x13-inch baking pan lightly with butter or cooking spray. This will prevent the cake from sticking.
• In a large mixing bowl, whisk together the all-purpose flour, baking powder, kosher salt, granulated sugar, and ground cinnamon until well combined.
• In another bowl, mix the packed brown sugar, diced apples, applesauce, milk, and melted butter. Stir until everything is well incorporated.
• Pour the wet ingredients into the bowl with the dry ingredients. Gently fold everything together until just combined; be careful not to overmix.
• Transfer the batter to the prepared baking pan, spreading it evenly.
• In a small bowl, combine the all-purpose flour, brown sugar, ground cinnamon, oats, and diced butter. Use your fingers or a fork to mix until crumbly.
• Evenly sprinkle the streusel topping over the batter in the baking pan.
• Place the pan in the preheated oven and bake for 35-40 minutes, or until a toothpick inserted into the center comes out clean.
• Once baked, remove the cake from the oven and let it cool in the pan for about 10 minutes. Then, transfer it to a cooling rack. Slice and serve warm or at room temperature.