Preheat oven to 350 degrees. Spray 2 6-inch round cake pans with non stick spray and then line the bottoms with parchment paper rounds.

In a medium bowl, whisk together the gluten free flour, xanthan gum, baking powder, salt, and sugar then set aside.

In a large bowl, whisk together the eggs, lemon zest, milk, oil, lemon extract, vanilla extract, and food coloring (if using). Then whisk in the lemon juice.

Pour the dry ingredients into the wet ingredients and mix until the dry ingredients are completely incorporated. Transfer the batter to the two prepared cake pans, dividing the batter evenly between the two.

Bake for 30-35 minutes or until done. When done, a cake tester will come out with a few moist crumbs attached, the center of the cake will spring back when gently pressed, and the cake will start to pull away from the sides of the pan.

Cool the cakes in the pans for 20 minutes then invert onto a wire rack to cool completely.

When the cakes are cooled, use a serrated knife to cut the cakes in half horizontally. To do this evenly, cut 1.5 inches into the cake around the entire cake before slicing all the way through. At this point, wrap the cakes in plastic wrap and freeze flat on a sheet pan at least 1 hour or until ready to assemble.

When ready to assemble, make the cream cheese frosting and tint 1/4 cup of the frosting yellow for decorating.

Frost 3 of the cake layers with a thin layer of frosting to crumb coat. Add about 1 cup of the frosting to a piping bag. Snip off the end of the bag (with about a 1/2 inch opening) and pipe a dam (a frosting ring) around the outside edge of the 3 frosted cake layers. Freeze for 10-15 minutes to solidify.

When the frosting has solidified, place 1 of the layers on a cake stand. Add a heaping 1/4 cup lemon curd to the center of the cake and use a spoon to spread the lemon curd evenly inside the frosting dam.

Place a second layer on top of the base layer and gently press to adhere. Fill the second layer with 1/4 cup lemon curd and spread evenly to the edge of the frosting dam. Repeat with the 3rd layer.

Place the remaining cake layer on top of the cake and gently press to stack, making sure each layer is stacked straight and the cake isn't leaning. Frost the cake with a thin layer of frosting to crumb coat and fill in the gaps between the layers. Refrigerate the crumb-coated cake for 20-30 minutes to set.

When the crumb coat is set, frost the cake with the remaining cream cheese frosting. To make the watercolor effect, use an offset spatula to paint a few spots of yellow around the bottom half of the cake. Use an offset spatula or the flat side of an Icing Comb to smooth the yellow into the white frosting. It doesn't have to be completely smooth, just blended.

I used an Ateco #829 Open Star Tip to pipe the detail on top of the cake. I smeared a small amount of yellow frosting streaks on the inside of the tip and piping bag to make the two-toned frosting. Hold the piping tip pointing straight down and pipe a dollop onto the cake and pull straight up as you stop squeezing.

Keep the cake refrigerated until ready to serve and bring to room temperature for 10-15 minutes before serving. Keep leftovers refrigerated.