For the baked rooibos tea cream, combine the cream, tea bags and vanilla in a saucepan over a medium heat and stir occasionally until hot, about 5 minutes.
Remove from the heat, cover and stand to infuse for 1 hour.
Preheat the oven to 160 C / Gas 2.5. Whisk the 105g caster sugar and yolks in a bowl until pale and creamy, about 3 minutes.
Remove the tea bags and reheat the cream over a medium heat until hot, then gradually pour onto the yolk mixture, gently stirring to combine.
Strain through a fine sieve into a jug, pressing to remove as many seeds as possible from the vanilla bean and discarding the bean afterwards.
Stand for 5 minutes, and then skim the foam from the surface. Divide evenly among six 250ml ovenproof glasses.
Place the glasses on a folded tea towel placed in a deep roasting pan, ensuring they are sitting level. Fill the pan with enough hot water to come two-thirds of the way up the sides of the glasses and cover with foil.
Pierce a few holes in the foil with a skewer to release the steam, then bake until set, but with a slight wobble, 30 to 35 minutes.
Whilst the custards are baking, melt the butter in a non-stick frying pan and add the apple. Sprinkle over the 15g sugar and cook over a low heat, turning occasionally, until the apples are tender and golden brown.
Remove the custards from the oven, remove the foil and stand in the water until cool, about 30 minutes. Remove from the water, dry the glasses and refrigerate until chilled and firm, 2 hours.
Divide the apples among the custards, top with lemon sorbet (if required) and serve immediately.