Make the lemon curd in advance, so that it has time to cool.

For the curd, combine yolks, zest, juice and sugar in a small saucepan.

Whisk to combine. Set over medium heat and stir constantly, making sure to scrape sides and bottom of pan.

Cook until mixture is thick enough to coat the back of a spoon, about 5-7 minutes.

Remove from heat. Add butter, one piece at a time, stirring until consistency is smooth.

Transfer the mixture to a medium bowl. Lay a sheet of plastic wrap directly on the surface to prevent a skin forming. Allow to cool then refrigerate. You can speed up this process by placing the bowl with the lemon curd in it into a larger bowl filled with ice. This recipe makes about 3/4 of a cup of lemon curd.

Make the cake. Preheat the oven to 350 degrees F. Spray two 8" pans with baking spray, line the bottoms with parchment, then lightly spray the parchment. Set aside.

Sift together cake flour, baking powder and salt. Set aside.

In a mixer with paddle attachment, combine butter, sugar and vanilla. Beat on low until fully combined then on high for another 3-4 minutes until light and fluffy.

Alternate adding flour mixture and milk to butter mixture, beginning and ending with flour mixture (1/3 of the flour, 1/2 milk, 1/3 of flour, 1/2 of the milk, 1/3 of the flour mixture)

Fold in shredded zucchini until fully combined.

Beat egg whites to stiff peaks, then fold into batter until no streaks of egg white remain.

Divide batter evenly between prepared pans and bake for 25-30 minutes or until toothpick comes out clean. My cakes took about 25-27 minutes.

Remove from oven and allow to cool in pans for about 10 minutes, then remove from pans and finish cooling on racks.

Make the cooked flour portion of your buttercream. Place the 3 Tablespoons of flour into a small sauce pan and place over medium low heat. Whisk in 1/4 cup of the milk insuring that all flour gets incorporated and you don't have lumps. You're creating a slurry. Slowly whisk in the remaining milk. Adding small amounts of liquid at a time will help you avoid any lump issues. Continue to whisk over the heat and continue whisking for 1 minute after the mixture begins to boil. Remove from heat. Transfer to a shallow dish to allow for faster cooling. Press a piece of plastic wrap on the surface to deter a skin from forming. Allow to cool at room temperature until it's just barely warm, then transfer to the refrigerator. It will become a soft solid mixture once it is cooled.

When the cakes are fully cooled and you are ready to frost your cake, make your frosting.

With a mixer, beat the two sticks of butter,vanilla and sugar until well combined and fluffy about 1-2 minutes. Slowly add spoonfuls of the cooled cooked flour mixture into the butter mixing well after each addition. After all of the cooked flour mixture has been added, continue beating the mixture until it is light and fluffy and the sugar is completely dissolved (check by rubbing some frosting between your fingers.) If the mixture looks curdled, it isn't done yet. Just keep mixing it until it all comes together.

To assemble cake, spread a little less than half of the frosting on top of your first layer staying about a half inch in from the cake edge. Spread half of the lemon curd on top of the frosting layer leaving a half inch to an inch from the frosting edge. Press a layer of fresh blueberries on top of the lemon curd. I fully covered the lemon curd with blueberries.

Spread a layer of frosting on the bottom side of the top cake layer, flip it over and press it on top of the blueberries so that the blueberries are sandwiched between the two layers of cake with frosting and lemon curd beneath them and just frosting above them.

Repeat the frosting and lemon curd layers on top of the cake, then press blueberries into the lemon curd. You can create a circular design as I have, or cover the entire top with berries.