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1
Preheat oven to 350F.
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2
Line standard muffin tins with paper liners.
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3
Sift together cake flour, baking powder, and salt.
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4
Stir vanilla into milk.
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5
With an electric mixer on medium-high speed, cream butter until smooth.
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6
Gradually add sugar, beating until pale and fluffy.
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7
Reduce speed to low.
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8
Add flour mixture in three batches, alternating with two additions of milk, and beating until just combined after each.
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9
In another bowl, with electric mixer on medium speed, whisk the egg whites until stiff peaks form (do not overmix).
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10
Fold one third of the egg whites into batter to lighten.
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11
Gently fold in remaining whites in two batches.
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12
Divide batter evenly among lined cups, filling each three-quarters full.
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13
Firmly tap the tins once on countertop to release any air bubbles.
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14
Bake, rotating tins halfway through, until a cake tester inserted in centers comes out clean, 18 to 20 minutes.
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15
Transfer tins to wire racks to cool 10 minutes; turn out cupcakes onto racks and let cool completely.
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16
Cupcakes can be stored overnight at room temperature, or frozen up to 2 months, in airtight containers.
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17
Divide buttercream into four portions; leave one untinted and tint remaining three to desired colors.
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18
Place each portion in a pastry bag fitted with a coupler.
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19
Using a small open-star tip (#20), pipe peaks: Squeeze gently while lifting the tip, then release at the halfway point, and draw up tip until icing forms a point.
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20
Starting with untinted buttercream, pipe a single peak in the center of each cupcake, then pipe more peaks in a ring around it.
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21
Switch to tinted buttercream; pipe rings of peaks around the plain, until you reach the edge.
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22
Refrigerate 30 minutes to allow frosting to set.
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23
Cupcakes can be refrigerated up to 3 days in airtight containers; bring to room temperature before serving.
