Recipe Rhubarb-Mascarpone Mousse Cake

A yellow cake is filled with jam and then artfully surrounded by rhubarb mousse using a larger springform pan as a mold. A jewel-like rhubarb frosting creates a finishing touch. If you have small tri-star strawberries or early wild strawberries to garnish the top, all the better!

Total time 4 1/2 hours
Makes 8 to 12 servings

INGRÉDIENTSCake
1 cup all-purpose flour
1 teaspoon baking powder
1/4 teaspoon salt
1/2 stick (4 tablespoons) unsalted butter, softened
1/2 cup sugar
1 large egg, at room temperature 30 minutes
1 teaspoon vanilla
1/3 cup whole milk
1/2 cup strawberry or strawberry-rhubarb jam
Rhubarb-mascarpone mousse:
2 pounds rhubarb, cut into 1-inch pieces (8 cups)
1 1/2 cup sugar, divided
1/2 cup water, divided
3 teaspoons unflavored gelatin (less than 2 packages)
1 cup (8 ounces) mascarpone cheese
3/4 cup refrigerated heavy cream
1 teaspoon vanilla
Vegetable oil for greasing pan

Glaze
1 1/2 teaspoons unflavored gelatin
3 tablespoons water
1 cup rhubarb syrup (see below)

Side Dish
A few small strawberries, such as tri-star or wild strawberries with leaves (optional)
Special Equipment
1 (9-inch) round cake pan; 1 round (10-inch) springform pan with removable bottom

PRÉPARATIONMake the Cake

1. Preheat the oven to 350°F and place the rack in the center.
2. Butter a 9-inch cake pan and line the bottom with a round of parchment paper.
3. Butter the paper, then dust the pan with flour, shaking off any excess.
4. Sift together the flour, baking powder, and salt in a bowl.
5. Beat the butter and sugar together on medium-high speed until pale and fluffy, about 2 minutes.
6. Beat in the egg and vanilla until fluffy and well blended, about 2 minutes.
7. Reduce the speed to low and add the flour mixture and milk alternately in 3 batches, beginning and ending with the flour. Mix until the batter is just combined. Do not overmix.
8. Spread the batter evenly in the pan and bake until the cake begins to pull away from the sides of the pan and a wooden toothpick or skewer inserted in the center comes out clean, 20 to 25 minutes (the cake will still be pale in color and not golden).
9. Cool for 10 minutes in the pan on a wire rack, then invert onto a wire rack and turn to cool completely right side up.

Make the mousse while the cake bakes

1. Combine the rhubarb, 1 1/4 cups of the sugar, and 1/4 cup of the water in a large, heavy-bottomed saucepan and cook over medium-high heat, stirring occasionally, until the rhubarb releases enough juice to almost cover the cake, 5 to 8 minutes. Reduce heat and simmer, stirring occasionally, until the rhubarb breaks down and reduces to about 4 cups, 25 to 30 minutes. Remove from heat.
   Pour the mixture through a large fine-mesh sieve set over a bowl, collect 1 cup of the syrup, and set aside. Transfer the rhubarb pulp to a separate bowl.
   Soften the gelatin in the remaining 1/4 cup water for 1 minute, then stir into the hot rhubarb mixture until dissolved.
   Place the bowl in a larger bowl of ice water and stir the rhubarb mixture until it cools to room temperature (do not let it sit on ice).
2. Beat together the mascarpone, heavy cream, and vanilla with the remaining 1/4 cup sugar until stiff peaks form.
3. Fold the cooled rhubarb mixture into the mascarpone mixture.

Assemble the Mousse Cake

1. Carefully cut the cooled cake in half horizontally, then spread the jam over the bottom half and reassemble.
2. Invert the bottom of the springform pan (to make it easier to slide the cake off the bottom), then lock it on its side. Lightly oil the bottom and sides of the pan with a little vegetable oil.
3. Arrange the cake in the center of the springform pan. Pour the rhubarb mousse into the pan over the cake. Smooth the top. Scrape the pan on the counter twice to remove any air bubbles and chill the cake, uncovered, until the mousse is set, at least 2 hours.

Make the Glaze

1. Sprinkle the gelatin over the water in a small, heavy-bottomed saucepan to soften, 1 minute. Heat the gelatin over low heat until dissolved. Remove from heat and stir in the reserved rhubarb syrup.
2. Pour the glaze over the chilled mousse, tilting the pan slightly to completely cover it with an even layer. Refrigerate, uncovered, until the glaze is set, at least 1 hour.

To Serve

1. Let the cake stand at room temperature for 30 minutes to soften slightly. Wrap a tea towel soaked in hot water around the edge of the pan for about 15 seconds. Run the tip of a thin knife around the edge of the pan, then gently unlock and remove the sides of the springform pan.

Cook's Notes

1. The mousse cake can be made 1 day in advance and refrigerated. Cover loosely with plastic wrap once the frosting has set (use toothpicks to keep the plastic wrap from touching the frosting, if necessary).