Line the bottoms of three 6-inch cake pans with a round of parchment paper and preheat the oven to 350 F/180 C.
Combine the fruity pebbles and buttermilk and set them aside.
Whisk together the flour, baking powder, and salt and set it aside.
In a stand mixing bowl, cream together the butter, oil, and sugar on medium speed for 3 minutes or until fluffy.
Whisk together the eggs, vanilla, and lemon extract then stream them into the mixing bowl, mixing well until completely combined. Scrape down the bowl.
Add a third of the dry ingredients and mix on low until almost combined then mix in half of the buttermilk. Continue alternating the dry ingredients and buttermilk, ending on dry, mixing until just combined.
Divide the batter evenly amongst the cake pans and use an offset spatula to smooth the tops. (about 370 grams in each pan)
Bake the cakes for about 26 minutes or until the tops bounce back when touched. Let them cool for 20 minutes on a wire cooling rack, then run a knife or offset spatula around the sides of the pan and remove each layer. Let them cool completely on the rack before frosting.