In a large heatproof bowl, whisk together the egg yolks, the Redpath® Special Fine Granulated Sugar, 3 tablespoons of the elderflower liqueur (45 ml), water, and the remaining ¼ teaspoon (~2 grams) salt, until mixture is homogeneous. Place the bowl over a large heavy-bottomed saucepan of just simmering water, ensuring that the bottom of the bowl is not touching the water. Continuously whisk (see Chef’s Tips) until sugar is dissolved, mixture is pale and doubled in volume, and reaches the ribbon stage. The mixture's temperature should register 160°F (71°C) on a thermometer; 10 to 14 minutes, depending on the distance of the bowl from the hot water.
Remove from heat, wiping the moisture off the bottom of the bowl with a kitchen towel. Continue whisking until the mixture has cooled to room temperature (see Chef’s Tips).
In the bowl of a stand mixer, using the whisk attachment (see Chef’s Tips), whip the heavy cream and the remaining ¼ cup (54 grams) of Redpath® Golden Yellow Sugar until thickened. Scrape down the bowl, add the remaining elderflower liqueur, and whip on medium to medium-high speed until medium peaks form.
Place about ⅓ of the whipped cream into the cooled custard. Quickly stir into the custard mixture to lighten. Add the remaining whipped cream and gently fold into the custard mixture until just combined.
Transfer ⅓ of the mixture into the prepared pan. Spoon and fold in half the cooled strawberry sauce into the remaining custard (about 3 to 4 folds). Add in the remaining strawberry sauce and fold again (3 to 4 folds); you want distinctive red swirls of strawberries.
With an offset spatula, smooth the top and tightly cover the pan with foil and place it into the freezer to chill; at least 6 hours, but preferably overnight.