Line a loaf tin with plastic wrap, leaving an overlap to fold over the semifreddo. Over a saucepan of gently simmering water, beat the egg and egg yolks with the honey in a bowl until the mixture is pale and thick. Whip the cream until thick, and then gently fold in the egg and honey mixture. Pour into the prepared loaf tin, and cover carefully with plastic wrap before putting it in the freezer for about 2–3 hours. Place the sugar and water for meringue in a small saucepan over a high heat. Bring to a boil, stirring continuously with a wooden spoon until the sugar has dissolved. Reduce the heat to medium and brush down sides of the saucepan with a wet pastry brush to prevent any sugar crystals from forming. Beat the egg whites with the cream of tartar in the bowl of an electric mixer fitted with a whisk attachment until soft peaks form. Bring the sugar syrup to 250°F, then increase the mixer’s speed to high and, with the motor running, pour in the hot syrup in a smooth, steady stream. When the syrup is completely incorporated, lower the speed to medium and continue to beat the meringue until it has cooled to room temperature (15–20 minutes). By this stage the meringue will be thick and glossy. For the toffee and apple topping, heat the sugar in a saucepan and melt until light brown in color. Place on a silicone mat, dipping mini apples into the mixture to coat them, and add crushed walnuts. Cut the semifreddo into desired shape and pipe on meringue mixture, using a blowtorch to caramelize the peaks. Top with cracked toffee and apple topping.