1-Step 1: Prepare Your Equipment and Ingredients Before you begin mixing, preheat your oven to 350°F (175°C). This temperature allows the cake to bake evenly without developing a thick crust or drying out. While the oven heats, prepare three 8-inch round cake pans by thoroughly greasing them with butter or cooking spray, dusting with flour, and lining the bottoms with parchment paper rounds. This triple layer of protection ensures your cake layers release cleanly every time. For perfectly flat cake layers, consider wrapping wet cake strips around the outside of your pans. These fabric bands insulate the edges, helping the cake bake evenly from edge to center and preventing the dreaded dome that requires leveling later.

2-Step 2: Sift and Combine Dry Ingredients In a large bowl, sift together the all-purpose flour, baking powder, and salt. Sifting isn’t just about removing lumps it aerates the flour and distributes the leavening agent evenly throughout, which translates to a more uniform rise and tender texture. Once sifted, whisk the mixture gently to ensure everything is well combined, then set it aside while you prepare the wet ingredients.

3-Step 3: Cream Butter, Oil, and Sugar In the bowl of a stand mixer fitted with the paddle attachment, combine the softened butter, vegetable oil, and granulated sugar. Beat on medium-high speed for 4 to 5 minutes until the mixture becomes noticeably lighter in color and fluffy in texture. This creaming process incorporates tiny air bubbles into the batter, which helps the cake rise and creates that beautiful, tender crumb everyone loves in a perfect funfetti cake. The combination of butter and oil might seem unusual, but it’s actually a brilliant technique. Butter provides rich flavor and helps with structure, while oil keeps the cake incredibly moist. Together, they create the best of both worlds a flavorful cake that stays fresh for days.

4-Step 4: Add Egg Whites and Vanilla With the mixer running on low speed, add the egg whites in three separate additions, allowing each portion to fully incorporate before adding the next. This gradual approach prevents the batter from curdling and ensures a smooth, emulsified mixture. Once all the egg whites are combined, add the vanilla extract and beat on medium speed for another 2 to 3 minutes until the batter looks fluffy and voluminous.

5-Step 5: Alternate Adding Dry and Wet Ingredients Now comes the crucial step that determines your funfetti cake’s final texture. With the mixer on low speed, add the flour mixture and buttermilk in alternating batches, beginning and ending with the flour. A good pattern is: one-third of the flour, half the buttermilk, another third of flour, remaining buttermilk, and finally the remaining flour. Mix only until each addition is just incorporated, stopping to scrape down the sides and bottom of the bowl as needed. Overmixing at this stage develops too much gluten, resulting in a tough, dense cake rather than the tender, delicate crumb you want.

6-Step 6: Fold in the Rainbow Jimmies Remove the bowl from the mixer and add the rainbow jimmies. Using a silicone spatula, gently fold them into the batter with just a few turns enough to distribute them evenly without overworking the batter. The goal is to keep those colorful sprinkles intact so they create the beautiful confetti pattern throughout your baked cake.

7-Step 7: Divide and Bake Divide the batter evenly among your three prepared pans, using a kitchen scale for precision if you have one. The batter should fill each pan about two-thirds full. Gently tap the pans on the counter two or three times to release any large air bubbles that could create holes in your finished cake layers. Bake at 350°F for 32 to 38 minutes, rotating the pans front to back after 20 minutes for even browning. Your funfetti cake is done when the tops spring back lightly when touched, the edges have pulled slightly away from the sides of the pans, and a toothpick inserted in the center comes out clean or with just a few moist crumbs.

8-Step 8: Cool the Cake Layers Let the cake layers cool in their pans for exactly 10 minutes long enough to set their structure but not so long that they stick. Run a thin knife around the edges to loosen any spots that might be sticking, then carefully invert the layers onto wire cooling racks. Gently peel away the parchment paper and allow the cakes to cool completely before frosting, which typically takes about an hour.

9-Step 9: Prepare the Vanilla Buttercream While the cakes cool, make the frosting. Beat the butter and salt in a clean mixing bowl on medium speed until very soft and creamy, about 3 to 4 minutes. With the mixer on low speed, gradually add the powdered sugar about one cup at a time, adding a tablespoon of heavy cream between additions to maintain a creamy consistency. Once all the sugar is incorporated, add the vanilla extract and beat on medium speed for 3 to 5 minutes until the frosting is light, fluffy, and spreadable. If the frosting feels too stiff, add more cream one tablespoon at a time. If it’s too soft, add more powdered sugar or refrigerate briefly to firm it up.

10-Step 10: Assemble and Decorate Place one completely cooled cake layer on your serving plate or cake stand. Spread approximately one cup of frosting evenly over the top, then place the second layer on top and repeat. Add the third layer and apply a thin crumb coat of frosting over the entire cake this initial thin layer seals in the crumbs so your final coat will be clean and smooth. Refrigerate for 15 minutes to set the crumb coat. Apply the remaining frosting to the top and sides of the cake using an offset spatula or bench scraper for smooth sides. For the signature funfetti cake look, gently press rainbow sprinkles onto the lower portion of the cake’s sides. Pipe decorative dollops of frosting around the top edge and finish with a generous sprinkle of rainbow jimmies on top.