Preheat the oven to 350F/177C and line two, 8-inch (20-cm) cake pans with parchment paper and spray the sides with a baking spray. Set aside.
Prepare the cake batter first. In a large mixing bowl, combine the eggs, oil, buttermilk, extracts and sugar. Beat on medium speed for a few minutes until the eggs are well beaten. In a separate bowl, combine the dry ingredients: flour, baking soda, baking powder and salt. Sift the dry ingredients into the batter, then mix on low speed for about 1 minute, just until incorporated.
Next, fold in just half of the diced strawberries into the cake batter, along with the zest of 1 lemon. Divide the cake batter evenly between the two pans and sprinkle the remaining diced strawberries over the top.
Bake the layers in the preheated oven at 350F/177C for about 38 to 40 minutes, or until a toothpick inserted into the center comes out clean. Remove the cakes from the pans and onto a wire rack to cool completely.
Next, prepare the lemon curd. It needs to be completely chilled before being used in the recipe! In a medium sized saucepan, combine the sugar, eggs and egg yolks. Whisk vigorously for 3 to 4 minutes, until the mixture is thick, pale and ribbons off the whisk. Stir in the lemon juice. Cook the curd over medium heat, stirring constantly with a spatula, for about 4 to 5 minutes, until the curd thickens to pudding-like consistency.
Remove the curd from the heat, whisk again to remove any clumps and add the butter in chunks. Allow the butter to melt completely, then add the vanilla and whisk until the butter is well incorporated. Transfer the curd into a bowl, cover well with plastic wrap and refrigerate.
Soften the butter at room temperature. It should be slightly soft to touch but not melted! Place the butter into a mixing bowl and beat on high speed for 6 to 8 minutes, until the butter is fluffy and pale white in color. Add the confectioner's sugar and mix for another 3 to 4 minutes. Add the extract, lemon zest, citric acid and food coloring last. Mix again for about a minute, until the frosting is smooth and uniform.
Assembling the Cake:
Make sure the cake layers are completely cooled before assembling the cake! Using a long, serrated knife, level the tops of each cake layer, then split each layer in half. You will have 4 cake layers. Transfer about 1 cup of the lemon buttercream into a pastry bag tipped with a round or star tip; I used Ateco tip #823.
Pipe a barrier ring of frosting around the edge of the cake layer before adding the filling. Watch my YouTube video to see how it's done. Fill the first layer with half of the crushed strawberries, the second layer with 1/4 to 1/3 cup lemon curd, and the third layer with the remaining berries.
Frost the top and sides of the cake with a thin crumb coat of buttercream, then chill the cake for about 20 minutes. Add the final layer of frosting, smoothing it with cake spatulas. Garnish the top of the cake with dollops of frosting and more lemon curd. Keep the cake refrigerated until ready to serve.
Garnish the top of the cake with strawberries and lemon wedges when ready to serve. Don't add them too early as they will dry out.