Preheat the oven to 200 degrees Celsius (390 Fahrenheit).
Place the fillet burgers on a baking tray and bake for 17-19 minutes until golden.
Peel and chop the onion, carrot and potato in a pan, heat up the oil on a medium heat, add the chopped onion, and fry until golden.
Add the chopped potato and carrot together with the garam masala, and give it a good stir, then leave it to cook for 1 minute for the powder to release its flavour.
Pour over the stock, and place a lid on the panleave it to cook for 10-15 minutes or until the veggies are tender.
Mix the cornflour with a tablespoon of water, and add it to the sauce.
Leave it to cook for a further 2-3 minutes for the sauce to thicken.
Add the sauce to a blender and blitz until smooth, then serve the crunchy fillet burgers on a bed of rice, and pour over the sauce.