If using fresh lemons, preheat the oven to its lowest setting. Thoroughly zest the lemons and spread the fresh lemon out on a parchment paper lined baking sheet.
Put into the oven on the lowest setting and leave until completely dried. Mine took about 70 minutes.
When completely dried, mix with the peppercorns and salt in a food processor until well mixed. If making with pre-dried lemon peel, just mix all ingredients in a food processor until blended.
Notes
Store in a tightly sealed jar or airtight container in the cupboard.