Spatchcock the poussins by cutting along the backbone and flattening them.
Rub birds with garlic, cayenne pepper, and sea salt.
Heat butter and oil in a skillet and cook poussins for 3 minutes cut-side down.
Flip and cook skin-side down for 5 minutes.
Cover with parchment, place a smaller pan on top as a weight, and cook for 25 minutes on low heat.
Boil chopped plums in a lidded saucepan with a splash of water for 10 minutes.
Mash plums and stir in garlic, paprika, treacle, and sea salt.
Simmer uncovered for 10 minutes then stir in the dill.
Rest poussins for 5 minutes while cooking herbs in the pan juices for 2 minutes.
Serve birds drizzled with herby juices alongside chutney and bread.