For the spiced plum crumble, preheat the oven to 180C/350F/Gas 4.
Heat a pan until hot, add the 40g/1¾oz of butter and all of the plums and cook for 2-3 minutes, or until the plums have just softened.
Add the brandy to the pan and carefully light to burn off the alcohol. (CAUTION: Keep clothing and flammable items well clear.)
Add the cinnamon sticks, star anise and cloves, then cook for for a further 3-4 minutes, until the plums have softened and broken down slightly.
Grease the insides of four 7.5cm/3in diameter 6cm/2½in tall chefs' rings well with butter. Wrap the sides and bases of the rings with aluminium foil, pressing firmly around the base to give a good seal.
Place the rings onto a baking sheet. Spoon the plum mixture into the bottom of the rings and pack down well.
Rub the 175g/6oz of softened butter and the sugar together in a bowl using your fingertips until the mixture resembles breadcrumbs.
Mix in the flour to form a crumble and sprinkle the crumble into the chefs' rings over the top of the plums, pressing down gently.
Transfer the baking sheet with the filled chefs' rings to the oven and bake for 15 minutes, until the crumble is golden-brown and cooked through and the filling is bubbling.
Meanwhile, for the plum brandy custard, whisk the egg yolks, sugar and plum brandy in a bowl until well combined.
In a separate pan, heat the milk, cream and vanilla pod in a saucepan until it just starts to boil, then reduce the heat and simmer for one minute.
Pour the milk mixture and the egg mixture into the bowl and whisk together until well combined.
Return the custard mixture to the saucepan and heat slowly over a low heat, stirring constantly with a wooden spoon, until the custard has thickened enough to coat the back of the spoon.
Remove the vanilla pod. (You can use wash and dry the vanilla pod and use it again in another recipe.)
To serve, lift the filled chefs' rings off the baking tray, and carefully remove the foil, placing one filled chefs' ring directly onto the centre of each serving plate. Carefully remove the chefs' ring from each crumble. Pour the custard to one side and finish with a spoonful of clotted cream.