Drape a piece of muslin or a new, slightly dampened, J cloth over a fine sieve or colander balanced over a bowl. Put in 400g of thick yoghurt, fold the edges of the muslin or cloth back over the yoghurt and set aside in the fridge for a good hour, overnight if you can. Set the oven at 180C/gas mark 4. For the crumble: put 100g of butter and 90g of demerara in the bowl of a food mixer and beat until thoroughly combined. Remove the bowl from the machine and rub in 80g of rolled oats, 1 tbsp of poppy seeds, 75g of plain flour and 1 level tsp of salt (I know this sounds like a lot of salt, but it makes the whole thing sing). Crumble the oat mixture on to a baking sheet – an assortment of different sized lumps is most welcome – and bake for 12-15 minutes until lightly crisp and pale biscuit-coloured. Remove from the oven and set aside. It will crisp as it cools. Halve 8 ripe-ish plums, remove their stones and place them cut side up on a baking sheet or grill pan. Drop small nuggets of butter (about 20g total weight) into the hollow of each fruit and grind over the tiniest amount of black pepper (just a few grains on each will suffice). Heat the overhead oven grill. Slip the plums into the oven and leave for about 20 minutes until soft and luscious. Place a spoonful of the strained yoghurt in shallow bowls (you need about 4 tbsp per person). Place 4 halves of plum on each then scatter with some of the crumble. You can save oven use by cooking both the crumbs and the plums at the same time.