Preheat oven to 375°F (191°C). Lightly grease a half-size baking sheet (12 x 17 inch) and line with parchment paper. Lightly grease parchment paper. Set aside.
In a small microwaveable bowl, melt butter at 10-second intervals until melted. Set aside.
On a piece of parchment, sift the cake flour and cornstarch to get rid of any lumps.
In the bowl of a stand mixer using the whisk attachment, whip the yolks, egg, the Redpath® Golden Yellow Sugar, vanilla extract, and salt on medium-high to ribbon stage. The resulting mixture should be almost tripled in volume, thick, and pale in colour; 5 minutes.
In a grease-free stainless steel or glass bowl, whip egg whites to soft peaks using a handheld mixer. At this point, slowly stream in the Redpath® Granulated Sugar while continuously beating. Increase speed to high and whip until stiff peaks form. Whites should be smooth and glossy; do not over whip.
Bring together two sides of the parchment together to form a tube, lift the dry ingredients, and sprinkle the sifted flour mixture over the surface of the whipped egg yolk mixture. Gently fold in until no streaks remain.
Fold in ⅓ of the beaten egg whites into the whipped yolk mixture. Add in the remaining whites, gently folding them into the mixture, being careful not to deflate the mixture by vigorously stirring it in; do not overmix.
Drizzle in the melted butter, quickly folding it into the batter.
Gently pour the batter onto the prepared baking sheet. Spread evenly with an offset spatula, with as few strokes as possible. Place into the preheated oven. Bake for 10 to 12 minutes or until the centre of the sponge springs back when gently pressed. If the indentation remains, bake for an additional 1 or 2 minutes.
While the sponge is baking, ready a tea towel and the Redpath® Icing Sugar.
Remove sponge from the oven. Take an offset spatula or paring knife and run it along the edges to loosen the parchment paper and/or sponge from the baking sheet. Sift the Redpath® Icing Sugar over the hot surface of the sponge. Place the tea towel onto the sponge. With the aid of oven mitts and another baking sheet (bottom side down) place onto the tea towel, flip the sponge cake over. Remove the hot baking sheet and carefully peel away the parchment paper from the bottom of the sponge.
Starting at one of the longer sides, roll the sponge into the tea towel. If possible, tuck the towel ends under to prevent the roll from unrolling. Cool completely in the tea towel; about an hour.
Carefully unroll the sponge. Turn the towel and sponge around and spread an even layer of the desired filling onto the cooled sponge, leaving about an inch of sponge at the long end free of filling.
Carefully reroll the sponge with the aid of the towel (without rolling in the tea towel) towards the filling-free end. Roll the Swiss roll in a piece of parchment or waxed paper, twisting the ends to prevent unrolling. Place roll, seam side down, onto a cutting board or baking sheet and place into the fridge to chill and firm up; at least 2 hours.
Remove from fridge, unwrap, garnish as desired and place onto a serving platter. With a sharp serrated knife, cut Swiss roll into 1-inch slices.
