If your slow cooker has a browning function do the following steps directly in your slow cooker, if not, use a large frying pan.
Heat oil in slow cooker or pan.
Add massaman curry paste.
Cook for about 2 minutes, stirring occasionally.
Add meat, stir to cover meat in the paste, continue cooking to allow meat to brown.
Once meat is browned (not cooked) add onions and potatoes - stir and cook for a minute or two.
At this point if using frying pan to brown, transfer to your slow cooker.
Add coconut milk and stir to combine.
Put lid on and slow cook for 4-6 hours depending on the type of machine being used - follow manufacturer’s recommendation for red meat. The 45-in-1 only needs 2 hours to slow cook red meat - this is preset into the machine, a regular crock pot or slow cooker will likely require 4- 6 hours.
Serve with rice and your choice of vegetables.