This Rhubarb Upside-Down cake has a brown-butter caramel topping, a spiced rye crumb, and a bright rhubarb glaze. One of the best ways to use spring rhubarb.
2tablespoonswhole milk()if needed for loosening batter)
Rhubarb glaze
1/2cuprhubarb(chopped)
1tablespoonwater
1tablespoonhoney
1teaspoonorange juice
Instructions
Preheat the oven to 350°F. Butter a 9-inch round cake pan and line the bottom with parchment paper.
In a small saucepan, melt 3 tablespoons unsalted butter with 1/3 cup light brown sugar, 1 tablespoon plum butter, 1 teaspoon finely grated orange zest1 teaspoon finely grated fresh ginger, and 1/4 teaspoon fine salt over medium-low heat, stirring until smooth.
Pour the caramel into the prepared pan, tilting it to coat the bottom evenly before adding the rhubarb.
Wash and trim 12 oz rhubarb. Discard the leaves (they are not edible) and trim away any dry or damaged ends. Cut the stalks into ½-inch pieces. Arrange the rhubarb pieces in a single, even layer over the caramel.
In a separate bowl, whisk together 1 1/2 cups all-purpose flour, 1/4 cup rye flour, 1 1/2 teaspoons baking powder, 1/2 teaspoon baking soda, 1/2 teaspoon salt, 1/4 teaspoon ground allspice, and 1/8 teaspoon ground cardamom.
In a large bowl, using an electric mixer on medium-high speed, beat 1/2 cup unsalted butter and 3/4 cup coconut sugar until light and fluffy, about 3 minutes.
Add 2 large eggs, one at a time, beating well after each addition.
Mix in 1 teaspoon vanilla extract and 1 tablespoon orange zest. Add the 3/4 cup sour cream
Add half of the flour mixture and mix. Add the remaining flour mixture and mix just until combined. If the batter seems very thick, add 2 tablespoons whole milk
Spoon the batter over the rhubarb and gently smooth the surface.
Place the pan in the preheated oven. Bake at 350°F for 40 to 50 minutes. The cake is done when the top is deep golden and springs back when lightly pressed.
Cool in the pan for 10 to 15 minutes.
Meanwhile, combine 1/2 cup rhubarb, 1 tablespoon water, 1 tablespoon honey, 1 teaspoon orange juice, and a pinch of salt in a small saucepan. Cook until the rhubarb breaks down, about 8 minutes. For a smoother glaze, blend or strain the mixture.
Invert the cake onto a serving wire rack. Optionally brush it with the warm rhubarb glaze.
Serve warm or at room temperature.
Notes
Use room-temperature eggs, butter, and sour cream. The batter comes together much more smoothly.Don't overmix the batter after adding the flour. Mix just until no dry streaks remain.Let the cake cool for 10 to 15 minutes before inverting. Too soon, and the topping may slide. Too late, and the caramel can stick to the pan.