Make the Cake. Preheat the oven to 350° F. Butter and flour the edges of 3 8-inch round cake pans and shake out the excess. Set aside. Line the bottoms of the pans with parchment paper.

In a medium mixing bowl, combine the cake flour, baking powder and salt. Whisk together and set aside. Add the butter to the bowl of an electric mixer fitted with the paddle attachment. Add the lemon zest to the bowl of the mixer with the butter. Beat on medium-high speed for 3 minutes, until light and creamy in color. Scrape down the sides of the bowl and beat for one more minute.

Add the sugar to the butter mixture, ¼ cup at a time, beating 1 minute after each addition. Mix in the eggs one at a time until incorporated. Scrape down the sides of the bowl after each addition. Combine the buttermilk and the lemon and vanilla extract in a liquid measuring cup. With the mixer on low speed, add the dry ingredients alternately with the wet ingredients, beginning and ending with the dry ingredients and mixing just until incorporated. Scrape down the sides of the bowl and mix for 15 seconds longer.

Divide the batter between the prepared baking pans. Bake until golden and a toothpick inserted in the center comes out clean, about 20-22 minutes, rotating the pans halfway through baking. Let cool in the pans about 10 minutes, then invert onto a wire rack and let cool completely.

Make the Frosting. Place the strawberries in a food processor or blender. Puree until completely smooth. Set the strawberry puree aside.

Combine the egg whites and sugar in a heatproof bowl set over a pot of simmering water. Heat, whisking frequently, until the mixture reaches 160° F and the sugar has dissolved.

Transfer the mixture to the bowl of a stand mixer fitted with the whisk attachment. Beat on medium-high speed until stiff peaks form and the mixture has cooled to room temperature, about 8 minutes. (The bowl should be cool to the touch.)

Reduce the speed to medium and add the butter, 2 tablespoons at a time, adding more once each addition has been incorporated. If the frosting looks soupy or curdled, continue to beat on medium-high speed until thick and smooth again, about 3-5 minutes more (or longer – don’t worry, it will come together!) Blend in the strawberry puree until smooth and completely incorporated, scraping down the sides of the bowl as needed.

Assemble the Cake. To assemble the cake, place one of the lemon layers on a cake board or cake platter. Top with a thin layer of strawberry jam. Gently place another lemon layer cake on top. Cover with another thin layer of strawberry jam. Top with the last layer of lemon cake. Frost the top and sides of the cake with the strawberry buttercream.

Make the Candied Lemon Slices. To make the candied lemon slices, wash and dry the lemons thoroughly. Use a sharp serrated knife to make very thin slices of lemon. Poke out any seeds in the slices with a toothpick. Combine the sugar and water in a medium saucepan over medium-high heat. Heat the mixture until the sugar dissolves. Add the lemon slices to the mixture so that they are in a single layer (none overlapping), reduce the heat to medium-low and let simmer about 20 minutes, turning the slices at least once so both sides are candied. Remove from the heat. Store in a container with the syrup until ready to use. Place on top of the cake just before serving.