Well done Kazzo! (I also put finely chopped carrot in my lasagne... A restaurant I used to work in used to finely process the carrot, onion and celery for their lasagne)

I know its "late", but another good bit of cheese sauce (or any white based sauce), is to have the milk warmed ("very" warm) before adding it to the roux (cooked butter and flour mix). That way you don't need to wait for it to heat through and start to thicken before adding the next bit of milk. That's what my Mum taught me about white sauce And my note, powdered milk works just as well (I always add a little extra powder to what the directions say).