Preheat oven to 200C.
Slice the chicken breasts in half, horizontally through the middle to give two pieces.
Place chicken in a single layer in an oven proof casserole dish.
Mix together the grated cheddar cheese, English mustard, Worcestershire sauce, beer, cayenne pepper and contents of the sachet of KNORR Three Cheese Pasta Sauce.
Spoon the mixture on top of the chicken breasts, scatter with cherry tomatoes and bake in the oven for 20-30 minutes until the chicken is cooked through and the rarebit topping is golden brown.
Serve with a salad.