Preheat oven to 200°C (400°F). Line a 10x15-inch (25x38 cm) jelly roll pan with parchment and lightly brush parchment with melted butter. In a clean bowl, whisk the eggs and granulated sugar vigorously by hand or with a mixer until tripled in volume, pale and ribbon stage (about 6–8 minutes electric, longer by hand). Stir in vanilla and a pinch of salt. Sift flour and cornstarch over the whipped eggs and fold gently in two additions using a flexible spatula, keeping as much air as possible. Pour batter into prepared pan and spread evenly. Bake 8–10 minutes, or until the sponge is set and lightly golden but not overbrowned.

As soon as the sponge comes out, invert onto a clean kitchen towel dusted with powdered sugar or onto another sheet of parchment. Peel off the lining paper. While still hot, roll the sponge gently from the short side with the towel/parchment inside to form the roll; this trains the cake to roll without cracking. Cool completely rolled-up on a rack.

Whipped cream filling

Chill a mixing bowl and whisk or beaters for 10–15 minutes (optional for better volume). Pour cold heavy cream into the bowl, add powdered sugar and vanilla. Whip to medium-stiff peaks — the cream should hold shape but still be soft enough to spread. Keep chilled until assembly.

French meringue (for topping)

In a clean, grease-free bowl, whisk egg whites with cream of tartar to soft peaks. Gradually add granulated sugar, a tablespoon at a time, while continuing to whisk until glossy, stiff peaks form and sugar is fully dissolved (rub a bit between fingers to check for grittiness). Use immediately to bake or torch as a topping.

Filling & assembly

Unroll the cooled sponge carefully. If you used a towel, remove the towel. Lightly brush the interior of the sponge with peach juice or light syrup to moisten (optional). Spread about two-thirds of the whipped cream evenly over the sponge, leaving a 1 cm (1/2 inch) border. Scatter chopped toasted walnuts and evenly distribute sliced peaches on top of the cream layer.

Gently re-roll the sponge without the towel, using the border to seal and form a neat log. Place seam-side down on a serving board. Trim ends cleanly with a serrated knife for presentation. Chill the roll seam-side down for 30–45 minutes to set.

Meringue topping & finishing

Remove the roll from the fridge. Spread the remaining whipped cream over the top and sides as a thin layer, or pipe decorative rosettes. Spoon or spread the meringue over the top where you want a toasted meringue finish. Using a kitchen torch, carefully toast the meringue until golden brown peaks appear. If you don't have a torch, place under a very hot broiler for 1–2 minutes, watching closely to prevent burning.

Garnish with extra walnut pieces and thin peach slices. Dust lightly with powdered sugar if desired. Refrigerate at least 15 minutes before slicing to help it hold shape.