For the Chocolate Cake

1. Preheat the oven to 350F. Grease two 8″ cake pans with baking spray, line with parchment paper and grease lightly again.
2. In a medium saucepan over medium-low heat, melt the chopped chocolate and butter until smooth. Set aside and let cool.
3. In a large bowl, combine the dry ingredients: flour, sifted cocoa powder, baking soda, baking powder, sugar, light brown sugar and salt. Whisk until fully incorporated.
4. In a separate bowl, whisk the eggs and egg yolk. Add the remaining wet ingredients and beat until smooth.
5. Mix the wet ingredients with the dry ingredients, and mix until there are no longer any clumps of flour.
6. Fold in the chocolate chips, if using.
7. Divide the batter amongst the 2 cake pans. I like to weigh the batter using a scale, to get even sized cakes.
8. Bake for 40 minutes, or until a toothpick inserted in the center comes out clean. 
9. Allow to cool for 10 minutes and transfer to a cooling rack.

For the Dulce de Leche Buttercream

1. In the bowl of a stand mixer with the paddle attachment, beat the butter and powdered sugar until creamy, about 5-7 minutes.
2. Start adding the kefir one tablespoon at a time, until desired consistency (I used 3 tbsp). 
3. Add 1/4 of the dulce de leche and beat until incorporated. Add another 1/4 and repeat until you’ve used up all the dulce de leche.
4. Add the vanilla and salt and beat. 
5. If the mixture is too liquid, add more powdered sugar. If it’s too thick, add another tbsp of kefir until you’ve reached the desired consistency.

Assemble:

1. Place the first chocolate cake layer, flat side up, on a plate or cake stand. Using an offset spatula, spread the top with the dulce de leche buttercream.
2. Place the second layer on top, rounded side up, and spread the buttercream evenly on the top. If you want to make swirls like I did, add the remaining buttercream to a piping bag with a star tip. Decorate in a half-moon style and add sprinkles!
3. Enjoy!