Make the yellow cake:
- Preheat oven to 350 degrees (or 320 degrees for convection). Grease two 9-inch round cake pans with butter.
- Sift flour, salt, and baking powder in a medium bowl and set aside.
- In a stand mixer fitted with paddle attachment, beat butter and sugar on medium speed until light and fluffy, about 3 minutes.
- Scrape down sides of bowl, and add eggs 1 at time, mixing after each addition. Mix in vanilla.
- Alternate adding ⅓ of flour mixture with ⅓ of milk at slow speed, until just barely incorporated.
- Bake until center bounces back to the touch, approximately 25 to 30 minutes. Cool in pan for 10 to 15 minutes and turn onto drying rack to cool completely.
Make the strawberry filling:
In a medium bowl, mix strawberries with sugar, then add vanilla and lemon juice. Mix well.
Make the strawberry buttercream:
- In stand mixer, beat butter until very smooth. Scrape down sides of bowl and add about 1 ounce of strawberry strawberry puree. Mix just to incorporate.
- Add sugar and remaining puree gradually. Mixture will be quite stiff. Finish by adding heavy cream as needed, beating until frosting is well mixed.
- Cut layers of cake in half horizontally with a serrated knife. Lay cut sides up and spoon strawberry filling onto each side.
- Carefully stack the cake layers back together so that the layers of strawberries are facing each other. Transfer to a cake stand.
- Frost cake with strawberry buttercream and decorate with any extra strawberries.