Preheat oven to 350F. Line 3, 8-inch cake pans with parchment paper; set aside.
In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy. Add the eggs, vanilla extract and lemon zest; mix until well combined. Add in the milk and whisk again.
In a separate bowl, combine all the dry ingredients: flour, baking powder and salt. Sift the dry ingredients into the batter using a fine-mesh sifter. Whisk the flour in by hand just until combined.
Divide the batter evenly into three portions, placing two of the portions into the prepared cake pans. Keep 1/3 of the batter in the mixing bowl. Melt the semi-sweet chocolate chips in a microwave or double boiler. Add the melted chocolate into the cake batter, whisk until smooth, then transfer into the last remaining cake pan.
Bake the cakes in preheated oven for 35 to 40 minutes, or until a toothpick inserted into the center comes out clean. Remove cakes from the oven and place onto cooling rack to cool completely.
Prepare the buttercream. Place the softened butter into a mixer bowl and whisk on high speed for 5 to 7 minutes until light and fluffy. Add the cream, vanilla extract and a few drops of blue gel food coloring; add more or less color to your liking. Begin adding the confectioner's sugar. Add 1 cup at a time and whisk well after each addition.
Assemble the cake. Spread the blueberry preserves onto the first cake layer, followed by a generous amount of the frosting. Use the chocolate cake layer as the second layer and top with lemon curd and frosting. Spread the frosting over the third layer and over the sides. Use a flat spatula to even off the sides and top of the cake.
Prepare the white chocolate ganache. Melt the white chocolate melts along with the cream in a measuring cup in the microwave. Allow the chocolate to cool slightly and thicken, then transfer the melted chocolate into a ziplock bag. Cut off the tip of the bag and pipe melted chocolate down the sides of the cake. Garnish the cake with fresh blueberries and mint leaves.
Keep cake refrigerated and remove from the fridge about 1 hour prior to serving to allow the buttercream to soften.