Winter Citrus Upside-Down Cake

To make the cake, preheat an oven to 375°F (190°C). Line the bottom of an 8- or 9-inch (20- or 23-cm) square cake pan with parchment paper. Spray the bottom and sides of the pan with nonstick cooking spray.

In a small saucepan over medium-high heat, combine 1/2 cup (4 oz./125 g) of the sugar and the water and bring to a simmer, whisking until the sugar is completely dissolved. Pour half of the syrup into the prepared pan. Arrange the orange, grapefruit and kumquat slices over the syrup, using half and partial pieces to fill in the gaps. Pour the remaining syrup over the citrus. Set aside.

In a medium bowl, whisk together both flours, the baking powder and salt. Set aside.

In the bowl of an electric mixer fitted with the flat beater, beat together the butter and the remaining 1 cup (8 oz./250 g) sugar on medium-high speed until light and fluffy, about 2 minutes. Add the eggs and beat until just combined, about 30 seconds, stopping the mixer to scrape down the sides of the bowl as needed. Add the orange zest and juice and vanilla and beat until combined, about 10 seconds. Stop the mixer and scrape down the sides of the bowl. With the mixer on medium-low speed, add the flour mixture in 2 additions and beat until just combined.

Pour the batter over the citrus in the pan and spread evenly. Bake until a toothpick inserted into the center of the cake comes out clean, 40 to 45 minutes, covering the pan loosely with aluminum foil if the cake starts to brown too quickly. Transfer the pan to a wire rack and let cool for about 20 minutes, then invert the cake onto a cake plate. Let cool for 10 minutes more.

Meanwhile, make the sweetened labneh: In a small bowl, whisk together the labneh, sugar and cream until very smooth.

Cut the cake into slices and serve warm or at room temperature with the labneh. Serves 6 to 8.

Williams Sonoma Test Kitchen