Can anyone tell me the best time and method of sowing Cowslip seeds?
Do I
put them straight in the ground or pot them to grow on? And when
should I
do it?

Like most species of Primula, they are best sown as soon as they are
ready to be shed from the parent plant. If already packeted, then I
guess substitute 'as soon as possible'.

Whilst they can fend for themselves in the open ground (indeed I have
them self-sow in the lawn, the pavement, the road, etc.), most people
trying to cultivate them less erratically would go for a pot first.

If in the UK (as one would expect in this newsgroup), then sow as soon
as possible in a pot, cover with a bit of soil, then grit/gravel to keep
rain/animals/etc. from disturbing the soil surface, and place outside.
They'll come up in the Spring.

--
Clarke Brunt