Traditional: 1 stick butter/margarinetraditional and sugar
Your favorite jam
Preheat the oven to 375° F with a rack placed in the center of the oven. Prepare a 9x13-inch jelly roll pan by lining it with parchment paper that has been buttered on both sides. Be sure to let the parchment line the sides of the pan; it helps to cut slits in the corners so that it fits into the pan neatly. Set aside.
In a large bowl, beat together the eggs, vanilla, and 3/4 cup sugar. Sift in the flour, baking powder, and salt and mix until combined. Set aside.
In a clean glass bowl or the clean bowl (see notes below) of an electric mixer fitted with the whisk attachment, beat the egg whites, starting on low speed to break up the whites until frothy. Add the cream of tartar and whisk until it begins to increase in volume. Increase the speed to medium, gradually adding the 1/2 cup sugar in tablespoon increments, until the egg whites are soft peaks. You'll know the meringue has reached soft peaks when you turn your whisk upside down, the meringue is starting to hold and the peak falls back down and droops.
Gently fold about 1/2 cup of the meringue into the batter, to soften and loosen the batter. Once this is combined, fold the remaining meringue in 3 increments - gently fold with a flick and wriggle of the wrist to incorporate the fluffy meringue into the batter without overmixing and deflating the batter. Transfer the batter to the prepared jelly pan, smoothing it with an offset spatula.
Bake for 13-15 minutes until the cake is golden, and a toothpick inserted in the center of the cake comes clean. Remove from oven and drop it from a 1" height onto a wire rack (to help prevent the cake from shrinking).
Let the cake cool to the touch (about five minutes). Once it is cool enough to handle, sprinkle the top of the cake with powdered sugar. Butter another piece of parchment paper and place buttered side down over the top of the meringue. Top with a light cutting board or another baking sheet and invert the cake onto a work surface. Carefully peel off the top parchment that was in the jelly roll pan. If you want a neater appearance, trim one of the short sides at a 45-degree angle (doing so will allow the cake roll to rest evenly seam side down). Using the parchment paper that is now on the bottom, carefully roll the warm cake from the short (untrimmed) end. Allow it to rest, seam side down, on a wire rack at room temperature until cool, about 1 hour.
Gently unroll the cake, and use an offset spatula to spread with your desired filling, leaving a 1/2-inch border around the cake. Roll the cake back up, and if needed, spread a little more filling into the ends. Wrap it back up in the buttered parchment and rest if not serving immediately.
Your filling of choice will determine how much time to rest/chill the cake. If you are using traditional softened margarine/butter and sugar, you can serve immediately. If you choose to fill it with jam, custard, or whipped cream, chill the cake in the refrigerator for at least 4 hours or overnight.
Trim the ends of the cake roll before serving for a neater appearance. Sprinkle the top of the cake roll generously with powdered sugar, slice, and serve.
Pianono Recipe Tips
Eggs: use very fresh eggs. Room temperature eggs are best when baking, however, eggs are easier to separate when cold. I recommend separating the eggs as soon as you retrieve them from the refrigerator into two separate bowls, then allowing them to come to room temperature (at least 30 minutes).
Bowls: use a very clean glass, metal, or copper bowl to whisk the egg whites. Any grease residue can prevent the egg whites from forming stiff peaks – for this reason, I strongly recommend that you avoid using a plastic bowl, which can harbor oily residue in its crevices. You can clean your bowl before using it by rubbing the bowl with vinegar or lemon juice, rinsing with water, and drying carefully.
Sugar: add the sugar gradually to the egg whites while whisking, one tablespoon at a time
Storage: Pianono can be stored in the refrigerator for 2-3 days.