In a bowl, whisk the flour with baking powder and salt; set aside until ready to use.

In a large bowl, mix butter with sugar and lemon zest until creamy. Add eggs, one at a time, beating until incorporated.

Add vanilla and lemon juice and mix until well combined. Reduce speed to low alternate adding flour mixture and buttermilk until everything is incorporated.

Place blueberries in a medium bowl, toss with 1 tsp of oil and 1 tbsp of flour.

Gently fold the blueberries into the batter, not too much as you don't want your batter to become blue. Only few folds will be enough.

Pour the batter evenly into the prepared pans.

Bake for about 30-35 minutes until a toothpick inserted into the center comes out clean.

Let pans cool on a cooling rack for 10 minutes.

Remove the cakes from the pan and let them cool completely.

Whisk constantly, for about 5 minutes, until it reaches 160F (71C).

Remove from heat and transfer to another bowl.

Start mixing on high speed for about 8-10 minutes, until glossy stiff peaks form. The mixture should be cooled before adding the butter.

With mixer on low gradually incorporate butter. Make sure butter is at room temperature otherwise will be harder to incorporate. Mix until smooth. Add lemon zest and lemon extract and mix to combine.

Place the rest of buttercream into a piping bag fitted with a ½ inch (1cm) tip.

Pipe about 4 vertical dots. Use a teaspoon to press and drag. Scrape the excess out of your spoon. Repeat until all the cake is decorated.

Refrigerate the cake. Before serving decorate with fresh blueberries and lemon slices and green leaves if desired.

Serve cake at room temperature and cut slices with a hot knife.