In a large mixing bowl, beat the butter and sugar with an electric mixer, until well combined. Add the eggs and yolks and beat for 1 min. Add the lemon juice and mix until blended - the mixture will look lumpy.

In a medium, heavy-based saucepan, cook the mixture over low heat until it melts. Increase the heat to medium and cook, stirring constantly, until the mixture thickens. It should leave a path on the back of a spoon and will read 170°F on a thermometer. Don't let the mixture boil. (Once it was completely melted, mine thickened and reached 170º in just a few minutes, so watch it closely.)

Remove the curd from the heat; stir in the lemon zest. Transfer the curd to a bowl. Press plastic wrap on the surface of the lemon curd to keep a skin from forming and chill the curd in the refrigerator. The curd will thicken further as it cools. Covered tightly, it will keep in the refrigerator for a week and in the freezer for 2 months.

In a medium bowl, whisk the cake flour, baking powder, lemon zest, and salt. Sete aside.

Using a stand mixer fitted with the paddle attachment, beat butter, sugar, and Jell-O. Beat on medium-high speed for about 3 minutes until light in color and fluffy.

With the mixer on medium speed, add the egg whites, one at a time, scraping down the sides of the bowl between additions. Continue to beat on medium-high speed for 2 minutes until smooth. Add the vanilla and stir to combine.

With the mixer on low speed, add in intervals, blending after each addition, ⅓ dry ingredients, ½ buttermilk, ⅓ dry ingredients, ½ buttermilk, ⅓ dry ingredients

Scrape down the bowl and mix for another 20 to 30 seconds.

Divide the batter evenly between the pans (16 ounces in each). Bake for 23 to 25 minutes, or until a toothpick inserted in the center of the cake comes out with just a few moist crumbs on it.

Remove the cake pans from the oven and let the layers cool in pans for about 15 minutes before inverting onto cooling rack to cool completely.*

Using a stand mixer fitted with the paddle attachment, beat butter and cream cheese for 3 to 5 minutes. Scrape down the bowl.

With the mixer on low speed, gradually add powdered sugar, mixing to combine after
each addition. Add cream, strawberry emulsion, and salt. Stir to combine.

Turn the mixer to medium-high speed and beat for an additional 3 to 5 minutes, scraping down the bowl at least twice during the process. The buttercream should be lighter in color and fluffy in texture.