Blend fresh herbs with coarse salt in a food processor or spice blender until fine. If you haven’t such an apparatus, mince your fresh herbs with an old-fashioned knife, and then blend with the salt. A good general proportion is an equal part fresh herb(s) to salt, by volume. For instance, if you are making a rosemary/thyme salt, add one cup of de-stemmed rosemary and thyme leaves to one cup of coarse sea salt. If your blend is heavy on herbs, and light on the salt, it might take a little longer to dry.
Spread the herb/salt mixture onto a serving tray or baking sheet and place in an area with good airflow. I like to place them on a table or counter under a ceiling fan. Depending on the ambient humidity, they may take two to four days to dry. The salt speeds up the drying process, simultaneously absorbing the flavor of the fresh herbs, along with the moisture.
If you need your salt blend right away, place it on a cookie sheet in the oven on the lowest setting with the oven door slightly ajar. Stir frequently and crumble up any clumps. Depending on the herbs used, it may take a few hours. Let cool and jar. This method will evaporate off some of the essential oils of the herbs, thus decreasing the aroma and flavor. Therefore, I prefer the slow drying method if you have the time.
If you are using dried herbs, you will skip the drying step, and use less of the herbs than a recipe calls for, as dried herbs are more concentrated than fresh.