This recipe makes 2 x 5″ cakes.

Ingredients
For the vanilla cake

90g (1/3 cup) soft butter
150g (3/4 cup) sugar
2 eggs, at room temperature
137g (1 cup + 1 tbsp) all purpose flour
3g (1/2 tsp) baking powder
3g (1/2 tsp) baking soda
3g (1/2 tsp) salt
100g (1/3 cup + 1 tbsp) buttermilk
3g (1/2 tsp) vanilla extract

For the Italian meringue buttercream

5 egg whites
230g (1 cup + 2 tbsp) sugar
74g (1/3 cup) water
340g (1-1/3 cup + 1 tbsp) butter

For the Oreo Cheesecake Filling

120g (1 cup) cream cheese
56g (1/4 cup) soft butter
50g (1/2 cup) oreo crumbs
30g (2 tbsp) sugar (optional)
5g (1 tsp) vanilla extract
+ 113g (1/2 cup) italian meringue buttercream (optional)

Method
For the Cake

1. Preheat the oven to 350F and grease and line two 5″ pans with butter and parchment paper.
2. In a stand mixer with the paddle attachment, cream the butter and sugar until pale and fluffy. In a separate bowl, sift and whisk the flour, baking powder, baking soda, and salt. Set aside.
3. In a separate small bowl, mix the buttermilk and vanilla together. Set aside.
4. Add in the eggs to the butter mixture and cream on medium speed until pale and fluffy.
5. Add in half the dry ingredients, mix for a few seconds until the flour is absorbed, add in the wet ingredients, stirring slightly, then adding in the rest of the dry ingredients. Mix on low until mostly combined, then blast on high speed for 30 seconds. Hand fold the rest of the batter until completely smooth.
6. Divide between the prepared pans and bake for 30 minutes or until a toothpick inserted into the centre comes out clean.

For the Italian meringue buttercream

1. Scale all your ingredients before you start.
2. Put your egg whites in a clean stand mixer with the whisk attachment. Set aside (but nearby your stove top or burner).
3. Put your sugar and water into a small saucepan on high heat, and using an instant read thermometer, bring the sugar syrup to 112C/234F.
4. Turn on your mixer on medium speed to start whipping the egg whites.
5. Continue to cook the sugar syrup and take off heat when it reaches 117C/243F.
6. Lower the speed on the stand mixer and carefully pour in the sugar syrup into the side of the mixer. Once all the sugar syrup is in the pot, gradually increase the speed of the mixer.
7. Whisk your meringue until it has cooled completely. Add your butter in chunks while the mixer is still whisking, about a heaping tablespoon at a time.
8. The mixture will start to curdle, keep mixing until the butter and the meringue come together.

For the oreo cheesecake filling

1. Mix the cream cheese and butter with a spatula in a medium mixing bowl until no clumps remain.
2. Add vanilla extract and the sugar if using.
3. Add in the oreo crumbs, and stir until fully combined.
4. Add in some italian meringue buttercream to ensure the filling sets (optional).