- Preheat the oven to 325 °F (160 °C). Have ready an ungreased 10-inch (25 cm) angel food cake pan.
- For the cake, place the 10 egg whites into a large mixing bowl, or in the bowl of a stand mixer fitted with the whip attachment. Add the cream of tartar and whip on high speed until foamy. With the mixer still running, add ¼ cup (50 g) of the sugar and continue to whip until the mixture forms a medium peak when the beaters are lifted. Set aside.
- Sift the flour, the remaining 1 ¼ cups (250 g) of sugar, baking powder and salt into a mixing bowl (or if using a stand mixer, you do not need to wash the bowl or whip attachment after whipping the egg whites). Add the lime zest, lime juice, oil and the 7 egg yolks. Blend on medium-low speed for a minute and then increase the speed to medium-high, whipping for about 2 minutes, until the batter is smooth.
- Fold the whipped whites into the batter in two additions (using a whisk allows you to fold easily without deflating the whipped whites).
- Pour the batter into the tube pan and bake for about an hour, until the centre springs back when gently pressed. Cool the cake in the pan, either upside down on a wire rack or, if the pan has “feet,” directly on the counter.
- To make the buttercream, place the egg whites and sugar in a metal bowl and set it over a pot of gently simmering water. Whisk constantly but not vigorously until the mixture reaches 150 °F (65°C) on a candy thermometer, about 6 minutes.
- Use electric beaters or transfer the mixture to the bowl of a stand mixer fitted with the whip attachment and whip on high speed until the meringue has cooled to room temperature (it will hold a stiff peak by then).
- With the mixer still running on high speed, add the butter a few pieces at a time. At first the meringue will hold its volume, then the buttercream will deflate a little and become very creamy yet fluffy looking. Beat in the raspberry purée, lime juice and vanilla. Set aside.
- When the cake has cooled and you’re ready to assemble it, run a palette knife around the inside edge of the cake pan. Insert a bamboo skewer down the inside of the centre hole in a few places, just to loosen the cake a bit. Tap out the cake onto the counter (you may have to tap it quite hard, but it will come out intact).
- To assemble the cake, use a serrated knife to slice the cake horizontally into three equal layers. Place the bottom third of the cake on a platter or a cake stand and spread the top of it with buttercream.
- Set the middle layer on top. Use a small palette knife to reach into the centre hole and spread a little buttercream on the edges of both layers of cake. Make sure it is well covered.
- Spread some buttercream on top of the middle layer of cake and then set the top layer on, pressing gently to ensure the cake is level.
- Spread some buttercream around the edges of the centre hole and then cover the top and sides of the cake completely. Chill the cake uncovered until ready to serve.
- To garnish the cake, make sure the raspberries are dry and at room temperature. Dip half of the raspberries into granulated sugar—the sugar will stick to the berries and look like a light coating of frosting. Alternate dusted and undusted berries in a circle on top of the cake, and insert a few mint leaves so the arrangement has the shape of a wreath.
Make Ahead: You can bake and assemble the cake a full 1 to 2 days before serving and store well wrapped at room temperature. Add the berry garnish no more than 4 hours before serving, otherwise the sugar on the berries will dissolve. Store the decorated cake uncovered in the fridge until serving time.
Helpful Hint: Use the buttercream at room temperature. When frosting the cake, it’s easiest to spread buttercream inside the centre hole at each layer using a small palette knife, rather than trying to do all three layers together once the cake is fully assembled.
From Set for the Holidays with Anna Olson, Appetite by Random House, 2018.