Brazo de Mercedes Recipe

Preheat oven to 350°F. 

Grease and line a 16x24x1-inch baking pan with parchment paper.

In the bowl of an electric mixer fitted with the whisk attachment, whip egg whites and cream of tartar on medium speed until frothy and starts to expand in volume.

Gradually add sugar. Whip until shiny, small bubbles appear, and soft peaks form. Stir in vanilla.

Using an offset spatula, spread meringue evenly on the lined baking pan. Lightly run a cake decorating comb or a fork on the surface of the meringue to create a ridged pattern.

Bake in the preheated oven for about 20 minutes or until set and top is golden brown.

Remove meringue from the oven. Dust the top generously with confectioners' sugar. Run an offset spatula along the edge of the pan to loosen the meringue from the pan.

Cover top with parchment paper then cover with a baking sheet. Invert pan to transfer meringue to the lined baking sheet.

Make the filling: Place egg yolks in a double boiler and stir using a wire whisk. (Make sure that the bottom of the pan on top does not touch the liquid in the double boiler. This will help prevent the eggs from heating up too quickly and turning into scrambled eggs.) Once warm and slightly thickened, add condensed milk and vanilla. Continue whisking gently until mixture thickens (like custard). Add butter, 1 tablespoon at a time; stir until well incorporated. Remove from heat.

Spread or pipe filling lengthwise on the center of the meringue. Lift a long end of the parchment paper and roll meringue into a log, enclosing the filling. Make sure the log is uniform in shape and thickness (use the parchment paper to adjust). Tighten the roll and keep covered in parchment until the custard has cooled. Unwrap and chill.