Make the Lemon Cake

• Preheat the oven to 350°F/177ºC. Prepare three 6-inch or two 8-inch cake pans by spraying the sides with baking spray and fitting a parchment paper circle to the bottom of each pan. Alternatively, you can grease and lightly flour the pans. 
• In a medium bowl, add the cake flour, baking powder, and salt and whisk to combine. Set aside. 
• In the bowl of your stand mixer (a handheld mixer works fine too!), beat the butter on high for two minutes until creamy. Add in the sugar and continue to cream on medium-high for another two minutes, scraping down the bowl and paddle as needed. Turn the mixer to low and add the eggs one at a time, mixing thoroughly after each addition. Add the sour cream, lemon zest, lemon extract, and vanilla extract. Turn the mixer to high and beat for 1 minute, scraping down the bowl and paddle once more. 
• With the mixer on low speed, add in the dry ingredients and mix until just combined. Add the milk slowly and mix until just incorporated. Scrape down the sides and bottom of the bowl and give it a few stirs to make sure there are no lumps. The batter will be slightly thick.
• Divide the batter evenly between the prepared cake pans and bake for 30-35 minutes. They’re done when they spring back to the touch and a toothpick inserted into the middle comes out clean. Let the cakes cool in the pan for five minutes before turning them out onto a wire rack for an additional few hours of cooling. Make sure they’re entirely room temperature before applying any frosting.

Make the Lavender Buttercream

• Add the whole milk into a small saucepan. Cook over medium heat, stirring frequently, until the milk begins to simmer. Remove from the heat and stir in the dried culinary lavender. Let the lavender steep in the milk for 15 minutes, then strain the milk through a fine mesh sieve set over a small bowl. Press all the excess milk out of the lavender buds before discarding them. Allow the lavender milk to cool completely before adding it to the buttercream.
• In the bowl of a stand mixer fitted with the paddle attachment (a hand mixer works fine too!) cream the butter on medium-high until it’s creamy and light in color, about 5 minutes.
• With the mixer on low speed, add the powdered sugar a few cups at a time, scraping down after each addition and making sure each cup is fully incorporated before adding the next one. Add the lavender milk, vanilla, salt, and food coloring (if using) and continue mixing on low speed until fully combined and smooth, scraping down the bowl and paddle as needed.
• Assembly
• Once the lemon cakes are completely cooled, level them to your desired height before filling and stacking with lavender buttercream. Crumb coat the cake with lavender buttercream, then place it in the refrigerator for at least 30 minutes to let the buttercream set firm.
• Frost the cake with a layer of lavender buttercream and smooth the sides with an icing smoother until level (don’t worry about creating an extra smooth finish for this one). Swipe a small icing spatula diagonally though the buttercream as you rotate the cake to create the texture pictured. Use the remaining lavender buttercream to pipe swirls on top of the cake with Wilton Tip 2D, leaving about 1/2 inch gap between each swirl. Sprinkle the swirls with more dried lavender and place a candied lemon slice between each one.