Empty contents of cheese sauce sachet into a jug and add 400 ml boiling milk.
Stir with a fork for 1 minute until thick and smooth and allow to stand.
Using a large saucepan, heat oil and add carrots and pesto and fry for 1 minute.
Add sachet of seasoning mix, 600 ml hot milk and uncooked pasta to the carrots and pesto.
Bring to the boil, stirring occasionally.
Reduce heat and allow to simmer uncovered for 10 min, stirring occasionally until the pasta is cooked.
Season with black pepper, remove from the heat and pour into an ovenproof dish.
Pour cheese sauce over and top with grated cheese.
Bake for 20 min until the cheese is golden brown.