Toast coriander seeds, cumin seeds and peppercorns in a frying pan over low heat, tossing or stirring frequently. You want the aroma of the spices to come out nicely before you take them off the heat. Allow spices to cool off for about 5 minutes.
Add to mortar with turmeric and grind. Set aside and put salt and chillies in the mortar and grind. Add back previous spices.
Add ginger and lemongrass and then the garlic and grind. Add kaffir lime leaves, coriander and shallots, pound and grind. Add shrimp paste and grind through.
It doesn’t matter if it’s not all completely ground to a paste if you’re going to give it a blitz. Add paste to food chopper or processor and blitz to get a fine paste. This will probably take a few minutes. Add your Thai red curry paste to your curry or store in the freezer for future use.