For the cake

Preheat the oven to 350 degrees F. Grease and flour two 8×2 inch round cake pans, lining the bottoms with parchment paper rounds.

Whisk together the cake mix, flour, sugar, and instant pudding mix to fully incorporate (at least 30 seconds).

In a separate bowl, mix together the water, eggs, sour cream, lemon juice, lemon zest, and lemon extract.

Add the wet mixture to the dry mixture. Using a wooden spoon, mix the batter together until fully incorporated. Do not overmix or the cake will be tough.

Evenly divide the batter between the prepared pans and bake for 30 to 35 minutes until a toothpick inserted into the center comes out clean or with just a few crumbs attached.

Cool in the pans 5 to 10 minutes then turn out to cool fully on a wire rack.

For the strawberry buttercream

Place the butter, strawberry purée, and lemon juice in the bowl of a stand mixer. Beat until the butter and purée are completely combined, scraping down the bowl to make sure everything is fully incorporated.

Add the powdered sugar to the mixing bowl. Mix on low until the sugar and butter are fully incorporated. If the frosting is too thick, add a little more strawberry puree. If it is too loose, add a little more powdered sugar (one tablespoon at a time).