Preheat the oven to 350 degrees F (180 degrees C). Grease and line three 6 inch cake pans with parchment paper.

In the bowl of a stand mixer fitted with the paddle attachment, combine the flour, sugar, lemon zest, baking powder, and salt.

Cut up the butter into small cubes and add to the dry ingredients. Mix on low speed until it resembles wet sand.

Add the oil, yogurt, milk, and vanilla, and mix until just combined.

In a separate bowl, whip the egg whites to stiff peaks. Gently fold it into the batter with a rubber spatula until just combined.

Divide the batter evenly between the prepared cake pans.

Bake for 28-32 minutes or until a tooth pick inserted comes out clean.

Cool completely before frosting.

Start with the pastry cream – heat the milk in a saucepan, and bring to a simmer or about 200 degrees F.

Whisk the egg yolks, sugar, and cornstarch together for 2-3 minutes until light in color.

Once the milk is simmering, slowly pour half into the egg-sugar mixture, whisking at the same time to temper the eggs.

Pour everything back into the saucepan and heat over medium heat, whisking constantly. After a couple minutes, a layer of bubbles will form over the top and it will begin to thicken.

Once the bubbles disappear, continue whisking for one more minute, then remove from heat.

Transfer to a bowl and cover with plastic wrap, pressing it directly up against the pastry cream to prevent a skin from forming. Chill for at least two hours or overnight. Alternatively, you could place the bowl of pastry cream over a water bath and whisk constantly until it cools down to 70 degrees F – you can immediately turn it into buttercream at this point.

If the pastry cream was chilled overnight, mix the pastry cream for about 10 minutes on low speed until it warms up to about 70 degrees.

Add the butter, a few cubes at a time, and beat on medium speed. If it looks curdled at all, continue beating on low speed until smooth.

Add the cream cheese, vanilla paste, and salt, and beat until fully incorporated.

Continue beating on low speed for several minutes until smooth.

Secure the first layer of cake on the cake stand with a small amount of frosting on the bottom.

Transfer some of the buttercream to a piping bag, then pipe a dam around the edge of the cake.

Spread about 3-4 tablespoon of jam in the center, then place the second cake layer on top and repeat.

Cover the whole cake in a thin layer of buttercream for the crumb coat.

Place in the fridge for about 20 minutes, then frost the cake as desired.

Top with fresh blueberries and lemon slices and enjoy!