Preheat oven to 350°F. Lightly brush two 9-inch round cake pans with room-temperature butter. Line bottoms of pans with parchment rounds; lightly brush parchment with butter.

 In a medium bowl, whisk together flour, baking powder, baking soda, and salt. In a large bowl, whisk together melted butter, oil, granulated sugar, and bananas. Whisk in eggs and vanilla until well combined. Stir in flour mixture in two additions, alternating with buttermilk and beginning and ending with flour.

 Divide batter between prepared pans (or use a jelly roll sheet pan and cut layers after baking) and bake until cakes are golden and a tester inserted in centers comes out clean, 35 to 40 minutes. Transfer pans to a wire rack; let cool 15 minutes. Turn cakes out onto rack, remove parchment, and let cool completely. Cakes can be frozen, tightly wrapped in plastic, up to 2 months.

https://www.marthastewart.com/1143786/banana-cake

Salted Graham Cracker Crumb

 5 graham crackers, finely crushed

1/3 c. all-purpose flour

1 tsp. kosher salt

¼ c. plus 1 tsp. granulated sugar

6 Tbsp. unsalted butter, melted

 Preheat oven to 325°F. Pulse graham cracker crumbs, flour, salt, and ¼ cup granulated sugar in a food processor until finely ground. Transfer to a medium bowl and add melted butter; mix until a few large clumps form. Spread out crumble on a rimmed baking sheet and bake, shaking once, until golden, 12–15 minutes. Let cool. Can be made several days ahead and stored in an airtight container at room temperature.

https://www.epicurious.com/recipes/food/views/peach-parfait-with-salted-graham-cracker-crumble

Caramel

1 c. granulated sugar

¼ c. water

150 ml heavy cream, room temperature

½ c. unsalted butter, room temperature

 Place sugar and water into a medium pot, stir to combine, but to not stir from this point forward. Cook over high heat, washing down the sides of the pot with a pastry brush dipped in water as needed to prevent crystals.

Cook until desired color of caramel is reached (amber) and immediately remove from heat. Very slowly pour in heavy cream while whisking quickly. The mixture will bubble up (a lot) and boil. Add butter, return to heat, and bring back to a boil. Cook for 2 minutes whisking constantly.

Remove from heat and let cool to room temperature. Transfer to a container and refrigerate to thicken. Bring caramel to room temperature before using.

Peanut Butter Italian Meringue Buttercream

360 g | 1¾ c. caster sugar

1 Tbsp. honey

100 ml | scant ½ c. water

180 ml | ¾ c. liquid egg whites or use 6 eggs

450 g | 4 sticks unsalted butter at room temperature cut into big chunks

¼- ½ c. unsweetened peanut butter powder

Put the sugar, honey and water in a deep saucepan stir to combine. Bring to the boil over high heat and check the temperature with a digital or jam thermometer. Cook until it reaches 120°C/ 248°F. (Personal note: prefer 248° to 235°-240°, as it yields a slightly firmer icing, and is more pipeable at room temperature.)

 Meanwhile, put the egg whites in the bowl of a stand mixer fitted with the whisk attachment. Whisk at maximum speed until you have soft peaks.

 Carefully pour the sugar syrup into the egg whites, while mixing, down the side of the mixing bowl. Continue to whisk for several minutes until you have a glossy meringue and the bowl feels barely warm to the touch.

 Add the butter, a few chunks at a time, and continue whisking at maximum speed until it is all incorporated. The buttercream may briefly separate or look curdled but keep whisking and it will soon become glossy and smooth.

 Beat in ¼- ½ cup peanut butter powder, to taste.

Base recipe, without PB powder: https://www.supergoldenbakes.com/chocolate-layer-cake-blackberry-italian-buttercream/

To assemble cake, spread one layer of cake with buttercream, top with 1/3 of the Salted Graham Cracker Crumb and repeat layers. Spread buttercream over top and sides of cake. (It may need to be reheated slightly, but not too much so it melts the buttercream. It should be a thick pourable consistency.) Drizzle caramel over the top edge of the cake, allowing it to drip down the sides. Pipe decorations around the top edge as desired and garnish top of cake with remaining 1/3 of the crumbs.