While the cake layers are baking and cooling, prepare the strawberry Swiss meringue buttercream. It’s important to start with a clean, grease-free mixing bowl—any residue can prevent the meringue from whipping properly. In a medium pot, bring about 1 inch of water to a simmer. Combine 8 egg whites and 2 1/2 cups of granulated sugar in a large metal mixing bowl and place it over the pot to create a double boiler. Make sure the water doesn’t touch the bottom of the bowl.
Constantly whisk the egg white and sugar mixture for about 3 minutes, or until it reaches a temperature of 160°F (71°C). You’ll know it’s ready if the sugar is completely dissolved and the mixture feels hot and smooth when rubbed between your fingers. Remove the bowl from the pot, wipe the bottom dry, and transfer the mixture to the bowl of a stand mixer. Whisk on medium-high speed for around 10 minutes, or until stiff, glossy peaks form.
Reduce the mixer speed to medium and add 2 cups of unsalted butter one stick at a time. The frosting will gradually come together into a thick, whipped consistency. If it appears curdled or broken, continue mixing—it should smooth out within 10 more minutes. If problems persist, refer to a Swiss meringue troubleshooting guide. Once the butter is fully incorporated, add 1/2 cup of strawberry jam, 1 tablespoon of freshly squeezed lemon juice, 1 teaspoon of vanilla extract, and 1/2 teaspoon of fine salt. Mix until fully combined, then add 1/2 cup of freeze-dried strawberry powder for additional flavor and color. Scrape down the bowl as needed. For a brighter pink hue, mix in a drop of red gel food coloring.
To create an ultra-smooth frosting texture, switch to a paddle attachment and mix on low speed for a couple more minutes. Transfer half of the frosting into a large piping bag and snip a 1-inch opening at the tip. Set aside until ready to assemble.