Heat your oven to 200°C/Fan 180°C/Gas 6. Halve the squash and scoop out the seeds. Pop it on a baking tray and slide into the oven. Roast for 45 mins till the squash is very soft and tender.
Tip the porcini into a small food processor, spice or coffee grinder and whizz to make a fine powder (see our tip if you don’t have one). Tip the powder into a bowl. Add most of the thyme leaves. Peel and crush the garlic and add to the bowl.
Stir ½ tbsp oil into the porcini bowl and mix. Smear both sides of the steaks with the porcini rub.
Fill a pan with water and bring it to the boil. Break the broccoli into small florets.
Warm a griddle or frying pan over a high heat. When it’s smoking hot, add the steaks. Fry for 1-3 mins on each side, depending on how well done you like yours. Slide them onto a warm plate. Cover with foil. Rest for 5 mins.
Add the broccoli to the pan of boiling water. Simmer for 5 mins. Drain well.
Take the squash out of the oven. Drain off any excess water. Scoop the flesh out of the skins and put in a bowl. Add 1 tbsp of the yogurt and some seasoning. Mash till smooth. Serve the steaks with the squash mash and broccoli. Sprinkle over the remaining thyme leaves to garnish.