Prep the pans and oven. Heat oven to 350°F (175°C). Grease your pans, line the bottoms with parchment, and lightly flour the sides. This prevents sticking and gives clean edges.

Mix dry ingredients. In a large bowl, whisk flour, sugar, baking powder, baking soda, and salt. This distributes leavening evenly for a level rise.

Cut in the butter. Add the softened butter to the dry mix and beat on low until it looks like damp sand with tiny crumbs. This coats flour with fat and creates a tender crumb.

Combine wet ingredients. In another bowl, whisk milk, sour cream, eggs, and vanilla until smooth.

Build the batter. Pour half the wet mixture into the dry and beat on medium for 30 seconds. Add the rest and beat another 30–45 seconds until smooth. Don’t overmix.

Add optional flavors. Fold in sprinkles for funfetti, cocoa and hot coffee for chocolate, or lemon zest and juice for a bright lemon version.

Fill the pans. Divide the batter evenly between pans and smooth the tops. For a 9x13-inch pan, pour it all in and level the surface.

Bake. Bake round layers 23–28 minutes, or a 9x13-inch cake 30–35 minutes. The cake is done when a toothpick comes out clean or with a few moist crumbs.

Cool completely. Let cakes rest in the pan 10 minutes, then turn out onto a rack, peel off parchment, and cool fully. Cold cakes frost cleaner.

Make the buttercream. Beat butter until light and fluffy, 2 minutes. Add powdered sugar in 2–3 additions, mixing on low, then medium. Add vanilla, salt, and cream to reach a smooth, spreadable consistency.

Assemble. Level cake layers if needed. Place the first layer on a plate, spread about 3/4 cup frosting, top with the second layer, and apply a thin crumb coat. Chill 15 minutes, then finish with a smooth final layer.

Decorate. Add sprinkles, simple swirls, fresh berries, or candles. Keep it fun and match the party vibe.