Preheat oven to 300°.
I use similar spice/salt/oil/herb mixture for making pork roast. You're simply combining the mixture and making a slurry to coat the chicken or meat.
For this recipe (the original recipe is by Carla Lalli) Coarsely grind the dry fennel seeds and red pepper flakes in a small spice mill or use your favorite mortar and pestle. Combine spice mixture with the chopped marjoram and thyme then add 1 tablespoons. salt, ½ tsp. pepper, and 3 tablespoons. oil in a small bowl. Rub chicken inside and out with spice mixture. Stuff chicken with the lemon chunks, both half heads of garlic and 2 of the marjoram and thyme sprigs. Using kitchen twine, tie legs of the chicken together to keep the herbs and flavorings from spilling out of the chicken.
You're going to roast the chicken in a rimmed baking sheet. Start by tossing the cut potatoes with remaining 3 tablespoons of oil and give them a good sprinkling of salt and pepper. Arrange the potatoes along the edge of the baking sheet and scatter remaining marjoram and thyme sprigs in center then place the chicken on top of the
Roast the chicken in the low heat oven, turning potatoes and basting chicken with the accumulated juices every hour, until skin is browned. The chicken and potatoes will be nicely browned and the meat will be almost fall-off the bone tender, about 3 hours.
Remove the pan from the oven and let chicken stand at least 10 minutes before you try to carve it. If you attempt to carve it any sooner it will just fall apart.
I was nervous about the potatoes getting overly cooked but they were perfection, creamy inside a little resistance as you pierce them with your fork.