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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
Whisk together flour, baking soda, baking powder, and salt.
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4
With an electric mixer on medium-high speed, cream butter and 1 cup sugar until pale and fluffy.
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5
Add eggs, one at a time, beating until each is incorporated, scraping down sides of bowl as needed.
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6
Beat in vanilla extract.
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7
Reduce speed to low.
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8
Add flour mixture in two batches, alternating with the sour cream, and beating until combined after each.
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9
Stir in 2 cups diced rhubarb.
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10
Divide batter evenly among lined cups, filling each three-quarters full.
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11
Bake, rotating tins halfway through, until a cake tester inserted in centers comes out clean, about 25 minutes.
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12
Transfer tins to wire racks to cool completely before removing cupcakes.
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13
Cupcakes can be stored up to 3 days at room temperature in airtight containers; remove liners before topping.
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14
To make rhubarb topping, use the tip of a paring knife to scrape vanilla-bean seeds into a saucepan, reserving pod for another use (such as vanilla sugar; see page 292).
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15
Add the water and remaining 1 cup sugar, and bring to a simmer, stirring to dissolve sugar.
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16
Remove from heat, and stir in remaining 1 cup rhubarb.
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17
Let cool completely.
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18
Remove rhubarb with a slotted spoon, and reserve.
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19
Return liquid to a simmer, and cook until reduced by half, 5 to 8 minutes.
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20
Let cool slightly, then return rhubarb to syrup.
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21
Once cool, rhubarb can be refrigerated in syrup up to 1 week in an airtight container; bring to room temperature before using.
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22
To finish, dollop a generous amount of whipped cream onto each cupcake, and top with rhubarb and some syrup.
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23
Serve immediately.
