Warming Mam bottles - any tips?

[MacMac123]

hi - my 4 week old was taking ages to feed so my health visitor suggested i switch from Avent to Mam bottles, which I've done. But is there a knack to warming these things? The base and valve are so thick that after standing in hot water in 5 mins the milk inside is still really cold. Anyone know if there is a knack to this?

Stick it in the microwave for 30 secs/1 min, perfect and v quick.

Or heat the milk up in a different vessel and then transfer to the mam bottle, obviously lots more steralising though.