Preheat your oven to 350°F (175°C).-Grease and flour two 9-inch round cake pans and line the line the bottom with parchment paper.
If making cupcakes - Line two standard size cupcake/ muffin pans with papers and set aside.
In a large mixing bowl, combine the flour, sugar, baking powder, baking soda, and salt. Whisk them together until well combined.
Add the oil (or ghee) and lemon zest to the dry ingredients. Using an electric mixer on low speed or a stand mixer fitted with a paddle attachment, mix the oil into the dry ingredients until the mixture resembles wet sand. This process is called "reverse creaming."
In a separate bowl, whisk together the milk,, eggs, lemon juice and vanilla extract until well blended.
With the mixer still on low speed, gradually pour about half of the egg mixture into the dry ingredient mixture. Mix until the ingredients are just combined. Scrape down the sides of the bowl with a spatula as needed.
Increase the mixer speed to medium and beat the batter for about 30 seconds. This will help to ensure that the batter is fully mixed.
Reduce the mixer speed to low again and gradually add the remaining milk mixture. Mix until the batter is smooth and well incorporated. Be careful not to overmix or whip too much air into the batter.
Set your batter aside to rest at room temperature for 30 minutes
Divide the batter equally between the prepared cake pans and smooth the tops with a spatula.
Place the pans in the preheated oven and bake for approximately 25-30 minutes for cakes and 20-22 minutes for cupcakes, or until a toothpick inserted into the center of the cakes comes out clean.
Once baked, remove the cakes/cupcakes from the oven.
Let the cakes cool in the pans for about 10 minutes and then remove to a wire rack to cool completely before filling and frosting.
Filling & Frosting
Evenly cut each cake layer in half to create 4 cake layers (you an also just leave as is for a 2 layer cake). I find a serrated bread or cake knife works best for this.
Pipe frosting around the edge of each layer to create a dam, and then fill with a thin layer of jam before topping with more frosting. Repeat with the next cake layer.
Frost and decorate your cake with the remaining buttercream.