Preheat oven to 350°F (175°C). Grease a 9x13-inch pan (or two 9-inch round pans).
In a bowl, whisk flour, baking powder, baking soda, and salt. Set aside.
In another bowl, cream butter and sugar until fluffy (~3 mins). Beat in eggs one at a time.
Mix in mashed bananas, buttermilk, and vanilla.
Gradually add dry ingredients, mixing until just combined.
Pour batter into pan(s) and bake for 30-35 mins (or until a toothpick comes out clean).
Cool completely before frosting.
Beat butter and peanut butter until smooth.
Gradually add powdered sugar, alternating with cream/milk, until fluffy. Mix in vanilla.
Spread frosting over cooled cake.
Top with crumbled bacon (if using), drizzle with caramel, and sprinkle chopped peanuts.