Making lasagne from cold bolognese-help!

[poshme]

I want to make a lasagne from some leftover cold bOlognese and am cheating by using a jar of White sauce. Do I need to heat the mince mix first or can I put it together cold and then cook it IYSWIM?
Essentially I want to save time...

Put it together cold, it'll heat through in oven.

Thank you! I thought I could but wanted a second opinion.
(obviously if we get food poisoning I'll blame you!)