Preheat oven to 350F and grease and flour three 4” cake rounds.

Whisk together flour, sugar, baking soda, salt, and baking powder in a bowl.

Add butter, and beat well with a hand mixer or in a stand mixer with the whisk attachment, until the mixture resembles fine crumbs.

In a separate bowl, whisk together egg, sour cream, vanilla and oil until combined.

Pour wet ingredients into the the flour and butter mixture, and beat on medium for 3-4 minutes. The mixture will be dry at this point.

Add in water and mix until just combined. Do not overmix.

Spread batter evenly into prepared pans. Smooth the tops with a spatula.

Bake for approx. 20-25 mins or until a toothpick inserted into the center comes out mostly clean.
Place cakes on wire rack to cool for 20 mins then turn out onto wire rack to cool completely before remove from pan.

Place egg whites and sugar into the bowl of a stand mixer, whisk until combined. 
Place bowl over a hot water bath on the stove and whisk constantly until the mixture is hot and no longer grainy to the touch or until it reaches a temparature of 165 degrees F on a candy thermometer. 
Place bowl on your stand mixer and whisk on medium-high until the meringue is stiff and cooled (the bowl is no longer warm to the touch (approx. 5-10mins)).
Switch to paddle attachment. Slowly add cubed butter and mix until smooth. Add vanilla and continue to whip until smooth.

Spread some buttercream on the cake board.

Place one layer of cake on a cake board and place in fridge for 5-10 minutes. This will help the cake stick to the cake board and not slip as you stack and frost.

Remove from fridge.

Top with approximately 1/3 cup of frosting and spread evenly

Repeat with remaining layers and apply a thin coat of frosting all over the cake for the crumb coat. Chill for 20mins.
Frost and smooth the sides.

Mark two vertical line on one side of the cake with a cake scraper or butter knife. This will mark the fault line.

Place cake in fridge for 20-30 minutes.

In the meantime, separate your small and large sprinkles.

Place approximately 2 tbsp of water in a bowl.

Remove cake from the fridge.

Dip the tips of your fingers in water before dipping them in the sprinkles. Stick small sprinkles into the fault line. Repeat until you have gone around the whole cake. Make sure to leave room for the larger sprinkles.

Fill a piping bag with frosting and pipe frosting above and below the fault line.

Scrape and Smooth with a bench scraper or offset spatula.

Once you’re happy with the look, place the larger sprinkles on the fault line.

Place cake in the fridge for another 20-30 minutes.

Pain the edges of the fault line with edible paint.

Enjoy!