Preheat the oven to 180C/170C fan/Gas 4. Cut the marrow in half lengthways. Using a spoon, scoop out the seeds, taking care not to remove too much flesh. Place on a baking tray, cut side up. Drizzle with 1 tbsp oil and season generously.
Crumble a stock cube into a heatproof jug. Pour over 750ml of boiling water. Stir to dissolve. Add a pinch of saffron and set aside to infuse.
Peel and chop your onion finely. Remove a clove of garlic from the bulb, reserving the remainder for the Grilled Veg Caviar & Garlic Cream recipe. Peel and grate or crush the garlic clove.
Heat 1 tbsp olive oil in a large heavy based pan. Add the onion and cook on a low heat for 5 mins until translucent. Add the garlic and cook for 1 min. Tip in the risotto rice and toast in the oniony oil for 2 mins.
Add in 2 ladlesful of the saffron infused stock. Stir. When it has been absorbed by the rice, add another ladleful. Repeat this process until all the stock has been used and the rice is al dente (soft with a slight bite). This will take 30-40 mins. Tip in the spinach leaves and stir in to the risotto until they have wilted.
Zest and juice the lemon. Strip the leaves from the thyme. Add half the lemon juice to the risotto. Add half the thyme leaves.
Tip the breadcrumbs into a bowl and add the lemon zest, remaining thyme leaves and plenty of seasoning. Scrunch together.Tip in the almonds. Pour the remaining lemon juice into the insides of the marrow.
Spoon the risotto into the roasted marrow halves. Scatter over the lemon and almond breadcrumbs. Place in the oven for 10 mins until the top is crispy and golden.