Make the lavender syrup. Add the water, sugar, and lavender to a medium saucepan. Bring to a boil and stir for 30 seconds or until dissolved. Remove from heat and let cool completely. Once it has completely cooled, pour syrup through a fine mesh strainer into a bowl and discard the lavender.

Preheat oven to 350℉. Grease and flour three 8'' cake pans and line the bottoms with parchment paper. Set aside.

In a medium mixing bowl, combine the flour, baking powder, baking soda, and salt. Whisk to combine and set aside. In a large mixing bowl, combine the eggs, granulated sugar, and brown sugar and whisk until smooth. Add the butter, vegetable oil, vanilla, and sour cream and whisk again until smooth. Add the milk and whisk until combined.

Gradually add the dry ingredients to the wet and mix with a rubber spatula until just combined. Pour the batter evenly into the pans and smooth out the tops with a spatula. Bake for 22-25 minutes or until a toothpick inserted comes out clean. Let the cakes cool for 10 minutes, then remove them from the pans and let cool the rest of the way on a cooling rack.

Make the buttercream. Add the butter to the bowl of a stand mixer and whip on medium high for 2-3 minutes until light and fluffy. Reduce speed to low and gradually add the powdered sugar until combined. Add the vanilla and milk and increase speed to medium-high and whip for 2-3 minutes. Add the salt and whip for another 2-3 minutes or until super fluffy. Scoop buttercream evenly into three bowls and add a drop of pink food coloring to one, a drop of yellow to another, and a drop of purple to the third. Mix each until completely combined. 

To assemble the cake, place one layer on a plate or the cooling rack (just so you don't mess up the plate you are serving on!). Spoon several spoonfuls of the lavender syrup over the cake, spreading it around and letting it soak into the cake. Let sit for a minute or two. Next, spread the top with one color of the frosting. Top with another layer and repeat with lavender syrup and spread top with the next color of frosting. Top with the third layer and repeat step with lavender syrup again (you won’t use all of the syrup) and spread with the third color of frosting, leaving a little bit left for the sides of the cake. Use the leftover frosting to "half" frost the sides, to create a "semi-naked" effect, using all three colors. I dotted the frosting randomly all over, so that the colors were evenly dispersed all over the cake. Use an offset spatula or bench scraper to smooth out the sides of the cake. 

Make the chocolate ganache. Place chopped chocolate in a medium bowl. Set aside. Place cream in a small saucepan over medium heat and bring to a simmer (do not boil!). Pour over the chopped chocolate and let stand until chocolate has softened, about 2-3 minutes. Stir until smooth and pourable. Let cool for a few minutes, then pour over the cake and let it drip down the sides. Decorate the cake with flowers if desired, and serve immediately!