For the baked rooibos tea cream, preheat the oven to 160°C/140°C fan/gas mark 3.
Combine the cream, tea bags and vanilla in a saucepan over a medium heat and stir occasionally until hot (5 minutes). Remove from the heat, cover and stand to infuse (1 hour).
Whisk the sugar and yolks in a bowl until pale and creamy (3-4 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 (30-35 minutes).
Whilst the custards are baking, melt the butter in a nonstick frying pan and add the apple. Sprinkle over the 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 (30-40 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.