Banana Layer Cake with Salted Caramel Filling and Peanut Butter Swiss Meringue Buttercream

BANANA CAKE

1. Preheat the oven to 350°f/180°c. Grease three 8” cake pans, and line with parchment paper on the bottom.
2. In the bowl of a stand mixer fitted with the paddle attachment, or in a bowl with an electric mixer, cream butter and sugar until light and fluffy. Add bananas and beat until incorporated. Add eggs one at a time, ensuring bowl is well scraped down and mixture is well combined.
3. Heat milk in the microwave, or a small pan until boiling. Add baking soda to milk, and add to the mix, mixing until well combined.
4. Sift flour, baking powder and salt, and add to the mixture. Mix briefly until just combined. Divide the mixture between the prepared pans (I like to do this by weight - see notes).
5. Bake the cakes for 35 to 45 minutes, checking for doneness after 35, or until a skewer inserted into the centre comes out clean.
6. Cool in their pans for 15 minutes then turn out onto a wire rack to cool completely.

SALTED CARAMEL FILLING

1. Place the sugar in a medium sized heavy bottom saucepan. Heat on medium, stirring constantly. The sugar will start to form clumps, then begin to melt.
2. Cook until is it amber in colour, then remove from the heat and immediately add all of the butter. Be careful as the caramel will bubble rapidly. Once the butter is incorporated, add the cream and whisk well to incorporate. Stir in the salt and vanilla, and pour into a glass jar. Allow to cool completely.

PEANUT BUTTER SWISS MERINGUE BUTTERCREAM

1. Place the egg whites, sugar and salt in the bowl of a stand mixer or a heat proof bowl. Place over a pot of simmering water, ensuring that the water does not touch the bowl.
2. Heat, whisking constantly, until the mixture registers 160˚f / 70˚c on a thermometer and the sugar has dissolved. Carefully transfer the bowl to the mixer, and fit with the whisk attachment.
3. Whip the egg whites on high until they are snowy white and fluffy, 8-10 minutes. Add the butter one chunk at a time. The mixture may look curdled - but just keep mixing! Once all the butter is incorporated, mix on high for a further 10 minutes. Add the vanilla and mix until incorporated.
4. Once the buttercream has finished mixing, and is smooth and silky, add in the vanilla bean paste. Mix for a further 2-3 minutes, then switch to the paddle attachment and mix on low for one minute to remove any air.
5. If you are making stripes on your cake, remove about 350g of the buttercream. Add the peanut butter to the remainder of the buttercream and mix well to combine. If you are not doing stripes, add the peanut butter to all of the buttercream and mix well to combine.

ASSEMBLY

1. Level off the cake layers. Transfer some of the peanut butter buttercream to a piping bag fitted with a medium round tip - this will be used to make a buttercream dam to hold in the salted caramel between layers.
2. Secure one of the layers of cake to a cake board or cake turntable using a little buttercream. Add about 1/2 cup of buttercream onto the first layer of cake, and smooth using an offset spatula. Create a buttercream dam using the buttercream in the piping bag by piping a ring of frosting around the outside edge of the first layer. Fill in the ring with some of the salted caramel, spreading to the edges.
3. Place the second layer of cake onto the first, pressing very lightly to secure, and sealing the joins with a thin layer of buttercream.
4. Repeat the layering process - add 1/2 cup of buttercream, make a dam, fill with caramel, then top with the third layer of cake - I like to put this one upside down to ensure that the top of the cake is flat. Return the rest of the buttercream in the piping bag to the bowl with the buttercream.
5. Crumb coat the cake - to do this, apply a thin layer of buttercream over the surface of the cake, and smooth with a bench scraper or icing smoother. Refrigerate the cake for 30-45 minutes, until the crumb coat has set. To ice without stripes (see notes): Cover the cake with a second, thicker layer of peanut butter buttercream. Smooth. Decorate as desired.
6. To ice with stripes: Apply a thick layer of peanut butter buttercream, and smooth completely, ensuring that there are no holes and it is completely smooth. Chill 15 minutes. Using a warmed icing comb (run under hot water then dry), go around the cake, creating grooves in your buttercream. Make sure that the grooves are sharp edged and deep - you may have to do a few passes to ensure this.
7. Freeze the cake for 30 minutes, then, using the reserved vanilla buttercream, place into a piping bag, and snip a hole off the end. Pipe buttercream into the grooves. Do not be afraid to overfill slightly. Once you have filled all of the grooves, smooth the cake using a warmed cake scraper, wiping between passes. Smooth off the top - the cake will be frozen so instead of scraping in toward the centre of the cake, I use my spatula to cut off the excess icing. Chill the cake for 10-20 minutes. To finish in the style that I have, place the remaining buttercream into a piping bag fitted with a Wilton 1M or other open star tip, and pipe a shell border design on the cake.
8. Store leftovers in the fridge either covered or in an airtight container. If you want to freeze cake, Freeze it until the buttercream is set (30 minutes or so), then wrap very tightly in plastic wrap and store in your freezer.