Heat oven to 200C / 400F.
In a large bowl, mix the tomato paste, olive oil, garlic, ginger and tikka masala spices to form a paste. Scoop just a spoonful of the mixture out (about 1/3rd of the total amount) and set aside, leaving the rest in the bowl.
Add the sweet potatoes, onions, and peppers, to the bowl. Mix and toss to coat the vegetables in the paste.
Finally, add the paneer and the remaining paste to the bowl and mix very gently just until the paneer is coated in paste too. You don't want to break the paneer pieces so go easy on them!
Spray a roasting tray with olive oil, then scatter the vegetables and paneer on top and add another spray (or drizzle) of oil over them.
Place in the oven for 35-45 minutes, until everything is lovely and charred and the sweet potato is soft inside.
Now remove the pan from the oven and very quickly add the garam masala and butter. Mix around, allowing the garam masala to toast from the residual heat of the pan.
Pour the tomato passata and cream into the dish. Give everything a stir until the sauce has formed.
Return to the oven for a further 5 minutes until the sauce is warmed through.
Scatter with cilantro (coriander) and serve!