Personally I use an ounce of trim per 250g of butter and do as follows.
1. add trim to water in pan and bring to boil, simmer for 10 minutes and stir continuously.
2.strain liquid reserving all liquid(which now has all the resin in it)
3.reduce liquid by boiling down to about equal volume of butter you want to mix with ie.250ml h20 to 250g butter.
4.add butter to water stir till melts.
5. freeze.
As both fat and resin will bond nicely together but not with the water you can seperate quite easily once frozen. By just adding kief to butter you wont get an emulsified end product, so certain cooking methods will cause burning of resin.Happy cooking!