Make mini sausages by pressing the skin of the sausages and twisting and cut the sausages with scissors. You’ve turned 6 sausages into 12 smaller ones - more to go around!
Peel, deseed, and dice the butternut squash into 2cm cubes and quarter the mushrooms.
Slice the red onions into wedges, trying to keep a section of the core so they stay in shape, and slice the leek into roughly 3cm/1" rounds.
Tip all the vegetables into a high-sided baking tray or large casserole dish, then toss with 2 tablespoons of olive oil and 1 tablespoon of chopped fresh sage. Put the tray in the top half of the preheated oven for 30 minutes.
Add the stock to a mixing jug and whisk in the two tablespoons of both maple syrup and wholegrain mustard.
After 30 minutes, remove the baking tray/casserole from the oven and pour over the stock mixture. Stir to coat everything and try to sit as many pieces of the sausage on top as possible. Return to the oven for 20 minutes.
Roughly chop the kale or cavolo nero, removing any tough stems, and mix it into the traybake along with the drained and rinsed can of lentils or beans. Taste for seasoning. Ensure the greens are in the liquid or underneath the vegetables as much as possible, and the sausages are sat on top
Return the tray/casserole to the oven for a final 10 minutes.
This step is optional, but it's a lovely crunchy contrast to the soft vegetables. Heat the remaining tablespoon of olive oil in a frying pan, then add the whole sage leaves and fry until crisp. Remove and drain on kitchen paper.
Serve up the traybake in large bowls, topping with the crispy sage leaves. This dish has everything you need, but if you wish to serve alongside some crusty bread to mop up the juices, that is totally allowed!
Notes
I've used good-quality pork sausages, but there is a wealth of flavours at the butchers. Venison would be great, and low-fat, or wild boar for example. Really, any good sausage will work here.
Feel free to use whatever seasonal vegetables you have in the fridge - such as turnip, celeriac, sweet potato. Simply cut them according to roughly how long they will take to cook.