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1
Heat oven to 350u00b0F
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2
Line 16 regular-size (21⁄2-in. diam) muffin cups with paper or foil liners.
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3
Stir flour, sugar, baking powder, baking soda and salt in a large bowl.
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4
Make a well in center; put oil, water, egg yolks, 3 Tbsp grapefruit juice and the grated peels in well.
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5
Whisk liquids to mix, then whisk with flour mixture just until blended and smooth.
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6
Beat egg whites in a medium bowl with mixer on high speed until frothy.
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7
Add remaining 1 tsp grapefruit juice; beat just until stiff peaks form when beaters are lifted.
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8
With a rubber spatula, stir 1⁄3 the beaten egg whites into the cupcake batter, then gently fold in remaining whites just until blended.
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9
Spoon 1⁄4 cup into each lined cup.
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10
Bake 15 to 18 minutes until tops are browned and a pick inserted near centers comes out clean.
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11
Cool in pan on a wire rack 5 minutes before removing to rack to cool completely.
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12
Beat ingredients (except grapefruit segments) in a medium bowl with mixer on low speed just to blend.
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13
On high speed, beat until smooth and fluffy.
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14
Finely chop 1 grapefruit segment and stir into frosting.
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15
Spread on cupcakes.
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16
Just before serving: Drain remaining grapefruit segments well and place on cupcakes; garnish with mint.
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17
NOTE: Can be made through Step 5 up to 3 days ahead.
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18
Refrigerate airtight.
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19
Section grapefruit up to 1 day before using; refrigerate covered.
