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1
Heat oven to 325 degrees.
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2
Line the bottom of a 9-inch springform pan with parchment paper.
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3
Butter the paper and sides of the pan.
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4
Wrap two layers of foil under the pan, and place it on a buttered baking sheet.
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5
In a medium bowl, mix rhubarb, cornstarch and 1/2 cup granulated sugar.
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6
Mix the brown sugar and 1/2 stick butter in a pan over medium heat.
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7
Whisk until smooth and bubbling, about 2 minutes.
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8
Sift together the cake flour, baking powder and salt.
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9
Whip 2 sticks butter in a mixer with a paddle attachment for 2 minutes.
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10
With your fingers, blend the remaining 1 cup sugar with lemon zest until the mixture is uniform in color.
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11
Cream together with the butter at medium-high speed until it is light and fluffy, about 4 minutes, stopping to scrape down the bowl halfway through.
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12
Add the vanilla and mix well.
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13
Add the eggs, one at a time, mixing well after each addition.
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14
Mix in the sour cream, then the lemon juice.
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15
(Its O.K.
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16
if the mixture looks curdled.)
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17
With the mixer set to low speed, add the flour mixture, 1/4 cup at a time, until well combined.
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18
Scrape down the mixer bowl in between the additions.
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19
Pour the brown-sugar mixture into the cake pan, then spoon in the rhubarb and its juices.
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20
Spoon in the batter so it covers all of the rhubarb.
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21
Smooth out the top.
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22
Bake for 1 hour and 15 minutes, or until the top of the cake is firm to touch and a toothpick stuck in the middle comes out without any large, moist crumbs.
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23
Place the pan on a wire rack, and cool for 15 minutes.
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24
Run a knife around the cake, place a plate on top of the pan and turn it upside-down.
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25
Release the cake from the pan while still warm or else it will stick.
