Once the sugar has reached 248ºF, with the stand mixer still running, slowly pour the sugar syrup into the whipped egg whites. Keep whisking until the meringue has formed soft peaks and is cool, then switch off the mixer.
Serving the pie: Carefully transfer the pie from its tin onto a serving board or plate. For a traditional looking pie with a surprise clear centre, pile spoonfuls of the meringue on top of the pie and use the back of a spoon to create billowing cloud shapes. Use a blow torch to brown the meringue, starting slowly and taking care not to burn it. Serve within an hour or two of adding the meringue.