Heat your oil in a large wide pan on the hob. Add your onions and thyme to the pan and cook very slowly for about 20 mins, putting the lid on so that they steam and soften, stirring occasionally so that they don’t stick to the base.
Meanwhile, bake your baguette slices on a baking tray in the oven for 8 mins until crisped up.
Remove your lid and turn the heat up. Cook your onions for another 10-15 mins until they are deeply caramelised, adding water occasionally to deglaze the pan.
Add the risotto rice and toast in the onions for 2 mins until starting to go translucent.
Turn down the heat. Pour your stock into the pan a little at a time, stirring until it has all been absorbed before adding another splash.
Once all your water has been added, you should have tender risotto rice. Add a third of your cheese, more thyme and season to taste.
Arrange your baguette slices on top of your risotto, then sprinkle on your remaining cheese.
Grill on a high heat for a couple of minutes until your cheese has melted.