In a medium saucepot over low heat, add 2 tablespoons oil. When the oil is hot, add the rosemary, onion, 1 clove chopped garlic, thyme, and juniper berries and stir well to combine. Sauté, stirring often, until the onions are soft; do not burn the garlic. Increase the heat to medium. Add the wine (if using) and reduce until dry. Add the stock, season with salt and pepper, and bring to a boil. Remove from the heat and transfer the contents to a blender (caution: liquid will be hot). Puree for 5 to 7 minutes, or until smooth. Reserve ¼ cup (60 ml) of the puree and pour the rest back into the pot. In a small bowl, combine the reserved puree with the arrowroot. Stir well to make a slurry and add to the pot. Stir well to combine and thicken the sauce.