Leave your frozen butter to soften at room temperature for a couple of hours, or use the quick-thaw method for softening butter (laid out in the recipe notes).
Once your butter is ready, prepare your fresh basil, rosemary, and oregano, and your garlic if using it. If you have an immersion blender and you plan to use larger amounts of butter at once, your ingredients don't need to be so finely chopped (see recipe notes).
Mash together the butter, herbs, salt, and garlic, using an immersion blender to better combine ingredients, if needed.
Use immediately, or if freezing, spoon the compounded butter onto a piece of wax paper or plastic wrap, forming all of it into a log and wrapping it well.
Make sure to flatten it and push out all air bubbles, and store it in another sealable bag. Place directly into the freezer and slice off pieces to use as needed.