Make Berry Sauce*: In a saucepan, combine 1 cup berries, lemon juice, and granulated sugar. Bring to a low boil and cook for 5-6 minutes, or until sauce has thickened into a syrup consistency. Stir in remaining 1/2 cup berries, remove from heat, then allow to cool completely before using. (Berry sauce can be made days ahead, stored in fridge).

Separate Eggs: Use cold eggs to separate the yolks from whites (easier to separate when they’re cold). Make sure NO egg yolk gets in with the whites, or they won’t whip properly. Set egg whites aside to come to room temp, about 15-minutes (room temp egg whites will whip to fluffier volume than cold ones).

Prepare Pan: Preheat oven to 320°F (160°C). Line a 18x13 inch bakers half sheet pan with parchment paper. (Parchment Tip: After making the meringue in next step, use a dot of it as “glue” to stick the parchment paper to the baking sheet.)

Beat Egg Whites: Grab a clean, dry mixing bowl then combine cream of tartar and egg whites. Use a hand mixer (or stand mixer) with a whisk attachment on high speed for 1-2 minute, until they reach soft peaks. With the mixer running, add sugar, a little at a time, mixing after each addition (should take about 5 minutes). Continue mixing until the egg whites are glossy and reach stiff peaks (about 1 to 4 more minutes). Stop mixing when the egg whites are glossy and at stiff peaks, to avoid over-beating them.

Add Cornstarch and Vanilla: Fold in cornstarch and vanilla using a rubber spatula.

Bake: Spread meringue on lined baking sheet in an even layer. Sprinkle sliced almonds over the top, if desired. Bake at 320°F (160°C) for 25 minutes.

Let Cool: Remove meringue from oven. Allow to cool for a few minutes, then sprinkle powdered sugar on top, and place a clean piece of parchment paper over it. Carefully flip the pan over so the meringue comes out onto the clean parchment, on your counter. Remove the bottom piece of parchment paper the meringue was baked on. Allow to cool completely before adding filling.

Mascarpone Whipped Cream: Mix cream, sugar, and vanilla until whipped into a fluffy cream. Gently fold in 1/2 cup mascarpone.

Assemble: Spread a little more than half of the whipped cream over the baked meringue. Smooth berry sauce on top.

Roll: Start at the short end and begin to roll the meringue (I like to pull the parchment paper towards me with one hand and roll the meringue with the other, to guide it along) into a log. Don’t worry if some of the outer layer crumbles or cracks—this is normal—the roll is meant to look rustic.

Garnish: Place roll, seam side down, on a serving tray. Use a spoon or pastry piping bag to decorate the rest of the whipped cream on top of the roll. Top with fresh berries and sprigs of mint or edible flowers. Refrigerate for 30 minutes if time allows, before slicing, or slice and serve immediately. Leftovers will keep in the fridge for a max of 1 day.