As soon as the parsnips are in the oven, place the dried porcini in a 4-cup measuring cup or bowl, and cover with hot tap water to the 3-cup mark. Set aside.
Heat enough olive oil over medium-high heat to generously cover the bottom of a sauteuse or large pan. Slide in the sliced shallots and leave without turning until the bottoms are browned. Stir, flipping them over, and again allow them to brown. After the first ten minutes add the minced garlic, thyme, and a 4-finger pinch of salt. Continue the browning process until the shallots are completely tender but not mushy, and have a good amount of browned caramelization throughout.
Stir in the flour, and continuously stir until the flour is well incorporated and beginning to stick to the pan. Stir for about three minutes.
Gradually ladle in the soaked mushrooms and their dark brown soaking liquid, stirring between ladlefuls, until it it incorporated. You will see the gravy begin to thicken immediately-- stir throughout this process to avoid any lumps.
Stirring frequently, bring the gravy to a boil, and add some more salt. There should be about one teaspoon total in the gravy, or to taste. Add a very generous amount of black pepper to season. Allow the gravy to bubble and thicken for about 6 minutes.