Can I substitute tomato puree for ketchup

[MamanPig]

A couple of tablespoons are needed for a veg lasgane I'm cooking and have run out of puree

yes of course

I do it all the time.

It isn't vital you know, just adds a richness to the tomato sauce.

Alternatively you can add another tin of tomatoes blended up and cook it on a low heat to reduce it (to act like tomato puree)

Great, thanks!

Just wanted to report back - made the substitution, and I'm afraid to say that it made the lasagne horribly sweet for me ... DD loved it though