Birthday Cake Muffins With Sprinkles and Quick Frosting

Birthday cake muffins are cake-style muffins made with creamed butter, vanilla and rainbow sprinkles, baked at 350°F (175°C) for 20 to 24 minutes and topped with a simple buttercream. This recipe makes 12 and can be baked the day before the party. It uses classic proportions and standard ingredients, so no special equipment is needed beyond a muffin tin and a mixing bowl.

Ingredients

For 12 muffins:

2 cups (250 g) all-purpose flour
2 teaspoons baking powder
1/4 teaspoon baking soda
1/2 teaspoon fine salt
1/2 cup (115 g) unsalted butter, softened
3/4 cup (150 g) granulated sugar
2 large eggs, at room temperature
2 teaspoons (10 ml) vanilla extract
3/4 cup (180 ml) buttermilk, at room temperature
1/3 cup (about 60 g) rainbow jimmies sprinkles, plus extra for the tops

For the quick frosting:

1/2 cup (115 g) unsalted butter, softened
2 cups (240 g) powdered sugar, sifted if lumpy
1 to 2 tablespoons (15 to 30 ml) milk
1 teaspoon (5 ml) vanilla extract
A pinch of salt

If you do not have buttermilk, several buttermilk swaps work in muffins and cakes, so you do not need to buy a carton for one batch.

Steps

Heat the oven to 350°F (175°C) and line a 12-cup muffin tin with paper liners. Set the rack in the middle of the oven.
Whisk the flour, baking powder, baking soda and salt in a medium bowl.
In a large bowl, beat the softened butter and granulated sugar for 2 to 3 minutes, until pale and fluffy. This step gives the muffins a finer, more cake-like crumb.
Beat in the eggs one at a time, then the vanilla.
Add the dry ingredients in three parts, alternating with the buttermilk in two parts. Start and end with the dry ingredients. Stir only until you no longer see dry flour.
Fold in the sprinkles with a spatula, using as few strokes as possible.
Divide the batter among the liners, filling each about two-thirds to three-quarters full. Scatter a few extra sprinkles on top if you like a bakery look.
Bake for 20 to 24 minutes, until the tops spring back lightly and a toothpick in the center comes out clean or with a few dry crumbs.
Cool in the pan for 5 minutes, then move to a wire rack. Let them cool completely before frosting, or the frosting will melt.
For the frosting, beat the butter for 1 to 2 minutes until creamy. Add the powdered sugar, vanilla and salt, then 1 tablespoon of milk. Beat on medium speed for 2 minutes, adding more milk a teaspoon at a time until it is spreadable but holds a swirl.
Spread or pipe the frosting onto the cooled muffins and finish with more sprinkles.

Choosing sprinkles that stay colorful

The type of sprinkle matters more than the amount. Choose rod-shaped jimmies for mixing into batter. They are made to hold their shape and most of their color in a moderate oven. Tiny round nonpareils and some natural-dye sprinkles tend to bleed into the batter and leave streaks, so save those for the top of the frosting, where they will not be baked.

Fold sprinkles in at the very end. Extra stirring spreads color and makes muffins tough.
Do not add much more than the 1/3 cup in the recipe. Too many sprinkles weigh down the batter and can make the crumb dense.
Check the label if anyone at the party has allergies. Sprinkles are often made in facilities that also handle other allergens, and ingredients vary by brand.

Variations

Sprinkle-top only: leave the sprinkles out of the batter and press them onto the frosting. This gives the cleanest colors.
Glaze instead of buttercream: whisk 1 cup (120 g) powdered sugar with 1 to 2 tablespoons milk and a drop of vanilla. Dip the cooled muffin tops and add sprinkles before the glaze sets.
Mini muffins: fill mini cups about two-thirds full and bake for roughly 10 to 13 minutes. Check early.
Almond note: replace 1/2 teaspoon of the vanilla with 1/2 teaspoon almond extract for the flavor many people associate with bakery birthday cake. Skip it if nuts are a concern for guests, as extract flavor can bother some people with nut allergies.

If you want to adapt the batter further, the basic muffin master batter and variation table shows how the ratios change when you swap in other flavors.

Storage and make-ahead

Unfrosted muffins keep in an airtight container at room temperature for up to 2 days. Buttercream made with butter and powdered sugar is generally fine at room temperature for a day or so in a cool kitchen, but in a warm room or for longer storage, keep frosted muffins in the refrigerator and let them sit out for 20 to 30 minutes before serving. Do not leave them in a hot car or in direct sun at an outdoor party.

To bake ahead, freeze the unfrosted muffins and frost them on the day. The guide to freezing muffins and thawing them so they taste fresh covers wrapping and thawing in detail.

Troubleshooting

Dense or tough muffins: usually overmixing after the flour goes in, or too much flour from scooping straight from the bag. Spoon flour into the cup and level it, or weigh it.
Flat tops: old baking powder is a common cause. Baking powder that is more than about six months open may be weak.
Streaky, muddy color: the sprinkles bled. Use jimmies in the batter and nonpareils only on top.
Frosting too soft: chill the bowl for 10 to 15 minutes or beat in a little more powdered sugar. Too stiff means add milk by the teaspoon.
Sunken centers: the oven door was opened too early, or the muffins were underbaked. Wait until at least the 18-minute mark before checking.
Living above 3,000 feet: cakes and muffins can dome and then collapse. See the notes on high-altitude baking adjustments before you change the recipe.

Quick answers

Can I use a cake mix instead?

A boxed mix will work in a muffin tin, but follow the package directions for muffins or cupcakes and the time on the box. This article’s recipe is made from scratch and the timings here apply to it.

Can I make these without buttermilk?

Yes. Use a standard buttermilk substitute, such as milk with a small amount of acid, or plain yogurt thinned with milk. The texture will be close to the original.

How many muffins does this make, and can I double it?

The recipe makes 12 standard muffins. It doubles well if you mix in a large bowl and bake in two batches, or two tins on separate racks, swapping their positions halfway through baking.

Why do the muffins need to cool before frosting?

Warm muffins melt butter-based frosting, which then slides off and soaks in. Cooling for at least 30 to 45 minutes on a rack gives a clean swirl.