Preheat the oven to 150-degrees and line a baking sheet with parchment paper.
Finely chop the rosemary and stir together with the salt in a small bowl. Pour the mixture onto the prepared baking sheet. Add the lemon zest and bake for 2 hours, stirring every 30 minutes.
Use the parchment paper to funnel the mixture into the food processor and pulse a couple times to combine.
Store in a tightly sealed jar. Makes about 2 cups and fits well in a 4oz mason jar.