Brown Butter Streusel: Cook butter in medium saucepan over medium heat until melted. Once melted, stir often until butter begins to brown and smell nutty, about 5 minutes. Remove from heat and add in pecans, sugar, cinnamon, and flour. Cool and reserve.
Cake: Heat oven to 350 degrees F. Grease a 9x13-inch baking pan.
Whisk together flour, baking powder, baking soda, cinnamon, salt, and sugar in large bowl.
Stir in melted butter, sour cream, milk, eggs, vanilla, and apples until smooth. Pour into prepared pan.
Sprinkle bacon on top of batter, followed by streusel.
Place pan in oven and bake for 30 to 45 minutes or until a toothpick inserted in the center comes out clean.