Preheat your oven to 350°F (175C/155C Fan) and prepare your cake pans. Grease and flour traditional pans or use silicone without preparation.

In a large mixing bowl or stand mixer, add the sugar and softened butter. Cream together on low until light and fluffy (about 2 minutes).

Add the eggs one at a time, beating after each addition.

Add the yoghurt, blueberry jam, lemon zest, and extracts. Beat lightly to combine into a smooth batter.

Sift the flour, baking soda, baking powder, and salt into the mixture and beat or stir until smooth and just combined.

Pour evenly into prepared cake tins and smooth the tops.

Bake in the center of the preheated oven for about 45 minutes, checking until a toothpick comes out clean.

Remove from oven and cool in the pans for about 5 minutes before transferring to a wire rack to cool completely.

Make the blueberry buttercream by mixing together the powdered sugar, melted butter, vanilla, and blueberry jam. Add milk slowly until desired consistency.

Level your cake layers by trimming any domed tops for flat layers.

Using about ¼ of your frosting, spread a layer of blueberry buttercream over the top of your base layer, then pipe a border around the outer edge about 1" thick.

Add about ¼ cup of blueberry jam inside this border and spread out for filling.

Invert your top layer with the trimmed side down and sandwich onto the blueberry jam filling.

Use remaining blueberry buttercream to frost the top and sides of the cake and top off with remaining blueberry jam.