Lemon Marshmallow Cake

Cake: Heat oven to 350 degrees F. Coat two 8x2-inch round cake pans with baking spray; line bottoms of pans with parchment or waxed paper.

Whisk flour, baking powder, baking soda, and salt in a medium bowl until blended. Beat butter, sugar, and lemon zest in a mixer bowl with paddle attachment on medium speed until light and fluffy, about 3 minutes; beat in egg, then egg whites and vanilla, until blended. With mixer on low, alternately beat in flour mixture and buttermilk until incorporated. Increase mixer speed to medium and continue to beat batter 2 minutes, until very smooth. Divide batter between pans and spread tops until level and smooth.

Bake 33 to 35 minutes, until pick inserted in centers comes out clean. Cool cakes in pans on a wire rack 5 minutes. Loosen edges of cakes with a knife and unmold onto rack; remove paper, invert cakes and cool completely on racks.

Lemon syrup: While cakes are baking, combine sugar and water in a small saucepan and bring to a boil. Simmer, stirring, until sugar is dissolved. Remove from heat; stir in lemon juice.

Filling: Beat cream and confectioners' sugar in mixer bowl with whisk attachment until stiff, with billowy peaks forming when beaters are lifted. Place Lemon Curd in a medium bowl and stir 1/2 cup of the whipped cream into it to loosen; then fold in remaining whipped cream until combined.

To assemble: Cut each cake layer in half horizontally using a serrated knife. Place one layer on a cake plate protected by strips of waxed paper; brush all over with lemon syrup, then spread one third of the jam (about 2 1/2 tablespoon) over to cover. Top with one third of the lemon cream and gently spread over jam layer. Top with another cake layer, brush with lemon syrup, then spread with preserves and more lemon cream. Repeat with the third layer. Brush the cut side of the last cake layer with lemon syrup and place cut side down on top of cake. Brush the top and sides of cake with any remaining syrup. (At this point the cake can be covered and refrigerated up to 1 day ahead before finishing with marshmallow topping.)

Marshmallow topping: Place egg whites, sugar, and cream of tartar in a large metal bowl. Set over a saucepan of simmering water. Whisk constantly until sugar is dissolved and whites are very warm to the touch, about 4 minutes. Transfer mixture to bowl of stand mixer. Beat 5 to 7 minutes, starting on low and gradually increasing to high until stiff, glossy peaks form. Beat in vanilla. Spread over top and sides of cake with a metal spatula in decorative swirls. Using a handheld butane crème brûlée torch, lightly brown the marshmallow topping. Serve immediately or refrigerate up to 2 days.