Preheat the oven to 220ºC/gas 7 and place roasting tray inside to heat up.
Pick the sage leaves, then roughly slice the dried cranberries. Peel and finely slice the onion.
Add the sage and cranberries to the pork meat, and crumble in the chestnuts. Season, then mix well and stuff into the cavities of each partridge, leaving enough space for the air to circulate around the filling.
Roll any leftover stuffing into balls. Rub olive oil, sea salt and black pepper all over the birds, then drape the pancetta or bacon over the breasts. Top each bird with a sprig of thyme, securing everything with string.
Put the partridges into the hot tray with a lug of ale and any stuffing balls, then cook for 15 to 18 minutes (depending on the size of your birds), then remove the partridges and stuffing to a warm plate, covering with foil and a tea towel – don’t wash the roasting tray though.
Meanwhile, put the lentils in a pan and cover with 2cm or so of water. Add the rosemary, remaining thyme, bay, unpeeled garlic cloves and the onion.
Squeeze the cherry tomatoes into the pan, if you’ve got them. Bring to the boil, then turn down and simmer for 12 to 15 minutes, or until the lentils are soft but holding their shape – the time will vary according to the type of lentil, so check the packet instructions.
At this point, you only want 1cm of water, so drain away any extra, then add a swig of extra virgin olive oil and the vinegar.
Fish out the herb sprigs and the garlic cloves. Squeeze the garlic flesh out of the skins and into the lentils. Mix up, then season to taste. Stir through the baby spinach, then put the lentils onto a platter.
Add the blueberry jam to the roasting tray and stir it into all the lovely bits from the bottom of the tray. Add a good swig of ale, then put the tray over a medium heat to thicken and reduce a little.
Take the partridges from the plate and put them and the stuffing, on the lentils. When the sauce is sticky, dollop some yoghurt over the lentils and pour the sauce over everything. Serve right away.