Preheat the oven to 300℉. While the oven is preheating, cut or tear the bread into one inch cubes and spread in a single layer on a parchment lined sheet pan.
Pop the sheet pan in the oven and let the cubed bread bake until it's completely dried out, approximately 30 minutes. Checking on them every few minutes to make sure they are not burning. Test their doneness by touching them with a spatula or wooden spoon, they should feel dry and crunchy. They should also crack apart when you break a piece. You don't want any moisture in the middle.
When they are finished in the oven, transfer to a food processor or blender. For finer breadcrumbs, pulse longer. The consistency of your breadcrumbs is a personal preference. I like my breadcrumbs a little finer; I find they are easier to work with.
After the breadcrumbs are processes to the consistency that you want them, you can now mix in additional herbs or leave them plain. If at this point, you feel like they need to bake longer, spread them back onto the sheet pan and bake until you get the desired golden crunchiness (with no moisture) you are looking for.
After the breadcrumbs have cooled, store them in a glass mason jar or other airtight container, either in a cool dry place, or in your freezer until you are ready to use them. They can be stored in the freezer for up to 6 months.