Pour milk into a large saucepan.
Heat over medium heat, until the milk begins to simmer.
Remove the pan from the stove top and add in the dried lavender.
Let the mixture steep for 15 minutes, then pour the liquid through a strainer into a small bowl.
Set aside to cool completely before using in the cake batter and frosting.
Preheat oven to 325°F. Line and grease four, 7-inch cake pans or three, 8-inch cake pans with parchment rounds.
Mix together all dry ingredients (cake flour, Domino Sugar® Golden Sugar, baking powder, and salt) in a stand mixer with a paddle or whisk attachment until fully combined.
Mix in chunks of room-temperature butter slowly into the dry mix, at a low speed. Continue to mix until no large chunks of butter remain, and the mixture becomes crumbly.
Pour in egg whites, and mix on low until just incorporated.
Add the sour cream, lavender milk, vanilla extract, oil and purple gel food coloring. Mix on a low speed until the batter is smooth an evenly colored.
Scrape down the sides of the bowl with a spatula, then beat on low speed for a few more seconds (the key is to mix until the ingredients are JUST incorporated, so that the batter isn't over mixed).
Divide the remaining buttercream evenly between five small bowls. Use gel food coloring to color the bowls of buttercream deep purple, pink, deep green, bright green and yellow.
Bake for 38-40 minutes, or until a toothpick comes out clean. Allow the pans to cool for 10 minutes, then run an offset spatula around perimeter of the pan to separate the cake from the pan.
Place cake layers on a wire rack to finish cooling.
Once fully cooled, use a serrated knife to level the tops, sides, and bottom of the layers, to remove any caramelization.
While the cake layers bake and cool, make the Golden Lavender Buttercream Frosting.
In a medium sized pot, add about 1 inch of water bring to a simmer.
Before making the frosting, be sure to thoroughly clean your mixing bowl; if there’s any grease it can make it difficult to make the meringue.
Add the egg whites and Domino Sugar® Golden Sugar into your clean mixing bowl.
Place the bowl on top of the pot filled with simmering water, being sure the water isn’t actually touching the bottom of your bowl. The bowl should create a seal over the pot.
Whisk the mixture constantly for about 3 minutes, until it reaches 160F. You can test the mixture to see if it’s ready by rubbing a tiny bit between your fingertips. The sugar should be fully dissolved, and it should feel super smooth and hot to the touch.
Lift your bowl away from the pot, and dry the bottom with a towel.
Lock the bowl into place on your stand mixer, and beat on medium high using a whisk attachment. Mix for about 10 minutes, until you have stiff and glossy peaks.
At this point in time, the bowl should be back to room temperature and no longer warm to the touch. If it’s warm, it will melt your butter!!
Once bowl is at room temp, swap out your whisk attachment for your paddle attachment.
Mix on a medium speed and add in the unsalted butter, 1 Tbsp at a time.
When all butter is mixed in, scrape the sides and bottom of the bowl with a rubber spatula and continue mixing for about 3 minutes. The frosting should have a thick whipped consistency at this point. If it looks lumpy or broken, keep mixing until it looks smooth and thick.
Add in the salt, vanilla extract, lavender milk and a drop of purple gel food coloring and mix on medium-high until fully incorporated. The buttercream should be a very light purple color. Set aside.
Stack and frost cake layers on a greaseproof cake board, using a dab of frosting to help stick the first cake layer to the board.
Add an even layer of buttercream between each cake layer.
Apply a thin coat of frosting around the cake, to fully cover the cake layers. Smooth using a bench scraper, then chill the cake in the fridge (10 minutes) or freezer (5 minutes) until the frosting is firm to the touch.
Add a second, thicker layer of frosting to the cake, and smooth using a bench scraper.
Color the remaining buttercream different shades of green, purple, pink, and yellow.
Place into separate piping bags, and pipe a floral design around the sides of the cake.
Make your cake layers in advance and freeze them: It breaks the process up and make it more approachable.
Make your frosting ahead of time too, or save any leftover frosting! It can be left out at room temperature for 1-2 days, stored in an airtight container in the fridge for up to a month, or in the freezer for up to 3 months. Be sure to give it a good stir once it thaws to get the consistency nice and smooth again.
A frosted cake can last in the fridge for up to a week, or in the freezer for up to a month. The buttercream locks in all the moisture, keeping the cake fresh and delicious!
If you cut into the cake and have leftovers, use any remaining frosting to cover the cut section to keep it moist and store in the fridge for up to a week.