This is not technically a Valentine’s Day post – February 14th just so happens to be the day I’m pressing “post” on something I’ve been working on veeeeeeeery slowly for the past 2 week. The only thing vaguely Valentine’s-y about it is that the inside is a little bit pink, but the point of today’s post is this: If you’re looking for a cake to put underneath your white chocolate peony, look no further. Without the peony, this cake looks plain on the outside but it is actually anything but – starting with the fact that it is flavoured with grapefruit. Lemon, orange and lime usually get all the citrus attention in baking, but replacing the lemon in lemon poppy seed cake with grapefruit and pairing it with white chocolate mousse frosting is pretty brilliant.
The original iteration of this cake is from none other than Martha herself (of course), who made it as a beautiful three layered torte using a slightly denser cake recipe. I came across her version years ago and when I was needing a cake to adorn with a giant chocolate flower, it came to mind because grapefruit just happens to be in season! I wanted my cake to be taller and not-so-dense though, so I used a different cake recipe and baked it in six-inch rounds to stack up into a tower. Not only does it taste really good (did I mention the white chocolate mousse frosting?), it also makes for a gorgeous slice of cake with the dusty blue-grey of the poppy seeds and pinky-orange of the grapefruit segments.
The only slightly tricky part of the cake is the frosting, which is basically white chocolate infused whipped cream, stabilized with gelatin. You have to chill the frosting long enough for it to be spreadable, otherwise it will just run off the cake as you try to assemble it. I had half the frosting in a metal bowl and the other half in a ceramic bowl, and I guess the ceramic bowl didn’t conduct the coolness of the fridge as well because that frosting took much longer to set up. It was just slightly too drippy when I used it to fill the cake, but I was able to salvage things by sticking a bbq skewer through the centre of the cake to secure the layers in place while it took a quick nap in the freezer to set. Totally worth the trouble!
White Chocolate Grapefruit Poppy Seed Cake
Inspired by Martha Stewart. Makes one 6 inch 4 layer cake, about 10 servings.
Grapefruit Poppy Seed Cake
Adapted from Under the High Chair.
Preheat the oven to 350˚F (325˚F convection). Line the bottom of 2 x 6 round cake tins with parchment paper, then grease the sides and flour the sides. Set aside.
In the bowl of an electric mixer fitted with the paddle attachment, cream together:
1/2 cup unsalted butter, soft
3/4 cup + 2 tbsp granulated white sugar
Beat until light and fluffy, then beat in:
2 large eggs (one at a time)
grated zest of 1/2 a grapefruit
In a small bowl, whisk together:
1 1/2 cups all purpose flour
1 1/2 tsp baking power
1/4 tsp fine salt
Reduce the mixer speed to low and add the flour mixture in 3 additions, alternating with 1/2 cup + 2 tbsp milk (start and end with the flour). Stir in 2 tbsp poppy seeds.
Divide the batter evenly between the 2 prepared cake tins, then wrap each one in a strip of wet towel to insulate it (this will help the cake layers bake evenly).
Bake in the preheated 350˚F (325˚F convection) oven for about 30-35 minutes, rotating the pans halfway through, until golden brown and a tester inserted in the middle comes out with a few moist crumbs sticking to it.
Let cool in the pan for about 20 minutes, then run a knife around the edges and invert the cakes onto a rack to cool completely.
White Chocolate Mousse Frosting
From Martha Stewart.
In a small bowl, sprinkle 1 1/8 tsp unflavoured gelatin over 2 tbsp water and set aside to soften.
Put 9 oz chopped white chocolate in a food processor and pulse to chop finely.
In a small saucepan, bring 1/2 cup + 2 tbsp heavy cream to a boil. Stir in the gelatin mixture to dissolve.
With the food processor running, pour the hot cream mixture over the white chocolate and process until smooth. Transfer to a metal bowl, cover with plastic wrap, then refrigerate until thick enough to hold ribbons (about 30 minutes).
Whip an additional 1 1/4 cups heavy cream to stiff peaks, then fold in the chocolate mixture. Scoop out 1 1/4 cups of the mixture into a separate bowl and stir in the grated zest of 1/2 a grapefruit.
Refrigerate until thick enough to spread, up to 3 hours (don’t let it set completely).
With a paring knife, cut the top and bottom off two grapefruits, slice off the rind from around the sides, and cut out each segment between the membranes (aka, supreme the grapefruit).
With a serrated knife, slices the two cake layers in half horizontally so you have 4 layers. Place one layer on a serving plate (protect the plate with strips of waxed paper) and spread with about 1/4 cup of the grapefruit zest white chocolate mousse. Arrange several grapefruit segments in concentric circles on top of the mousse. Top with a second layer of cake, cut side down so that it can soak up any excess juice from the grapefruit. Repeat with the remaining mousse, grapefruit segments, and cake layers. Use any remaining grapefruit zest white chocolate mousse to give the sides of the cake a crumb coat. If the frosting seems a little soft, secure the layers with a bbq skewer. Place the cake in the freezer for 15-20 minutes, until fairly solid.
Use the remaining plain mousse to frost the top and sides of the cake, spreading it smoothly with a spatula. Remove the wax paper strips protecting the cake plate, and chill the cake until firm.
Top it with a white chocolate peony, if you wish.