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.
In a large bowl, whisk flour, baking powder, baking soda, cinnamon, salt, and sugar together.
Stir in melted butter, sour cream, milk, eggs, vanilla, and apples until smooth. Pour into prepared pan.
Sprinkle crumbled 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.
Optional: Add an extra degree of difficulty (and flavor) by pouring out half the batter in the cake pan, then adding a layer of streusel before adding the final half of batter and another layer of streusel on top--as pictured.
In a medium frying pan over medium-high heat, cook bacon, turning slices as needed, until browned on both sides and crisp. Transfer to paper towels to drain. When cool enough to handle, crumble bacon.
Cut each egg in half lengthwise; gently scoop out yolks and place in a bowl. Mash yolks with a fork, then stir in mayonnaise, green onions, mustard, and crumbled bacon until well blended. Add salt and pepper to taste.
Spoon or pipe about 1 tablespoon yolk mixture into the hollow of each egg-white half. Serve immediately or cover and chill up to 4 hours.