Make the cake: Preheat the oven to 350 degrees F. Lightly brush an 11-by-17-inch rimmed baking sheet with vegetable oil and line with parchment paper. Brush the parchment with oil and dust with flour, tapping out the excess. Whisk the flour, 3/4 cup granulated sugar, the malted milk powder, cocoa powder, baking soda, cinnamon, allspice and nutmeg in a medium bowl; set aside. Beat the egg whites in a large bowl with a mixer on medium speed until foamy, 1 to 2 minutes. Increase the mixer speed to medium high and gradually add the remaining 2 tablespoons granulated sugar; continue beating until stiff shiny peaks form. Set aside.
Beat the vegetable oil, egg yolks and milk in a separate bowl with the mixer on medium speed (no need to clean the beaters). Reduce the speed to low and beat in the flour mixture until just combined. Fold one-third of the beaten egg whites into the batter, then fold in the rest until incorporated. Pour the batter onto the prepared baking sheet and spread evenly with a rubber spatula. Bake until the cake pulls away from the sides of the pan and springs back when lightly pressed, 12 to 14 minutes. Dust the cake with the confectioners' sugar and spread a large clean kitchen towel (not terry cloth) on top. Invert a cooling rack onto the towel, then invert the cake onto the rack; peel off the parchment. Roll up the cake and towel together, starting from a long side to form a 17-inch-long roll. (You'll remove the towel later.) Set aside on the rack to cool completely.
Make the frosting: Combine the granulated sugar and 3/4 cup water in a small saucepan and bring to a boil, stirring to dissolve. Cook over medium heat, without stirring, until a candy thermometer registers 240 degrees F, 20 to 30 minutes. (Brush any sugar crystals off the side of the pan with a wet pastry brush.) When the sugar has almost reached 240 degrees F, beat the egg and egg yolks in a stand mixer with the whisk attachment on high speed until thick and fluffy, about 5 minutes. Reduce the speed to low and slowly pour in the sugar syrup between the whisk and the side of the bowl. Increase the speed to high and beat until the bowl is cool to the touch. Remove the whisk and fit the mixer with the paddle attachment. With the mixer on medium-high speed, gradually add the butter and beat until thick and glossy. Combine the malted milk powder, vanilla and 1 teaspoon water in a small bowl; beat into the frosting along with the nutmeg.
Unroll the cooled cake and spread with 1 1/2 cups of the frosting. Gently reroll the cake (without the towel) and trim the ends. Cover with the remaining frosting; dust with cocoa powder.
Photograph by Johnny Miller
This style of frosting, a French buttercream, will always be a little softer than other styles of frosting due to the high volume of egg yolks and butter. Make sure the egg yolk/sugar syrup mixture is completely cooled before you start adding butter. If your frosting is too soft to spread after all the butter is beaten in, chill until it's firmed up enough to spread and then briefly rebeat it.
Courtesy of Food Network Magazine