Heat the olive oil in a sauce pan over medium-high heat.When the oil begins to shimmer, whisk in the flour. Whisk constantly for about 1-2 minutes until the flour begins to smell a bit nutty.Add the nutritional yeast and continue to whisk for one more minute.Add ½ cup of the broth and whisk into the flour mixture so that it is smooth and there are no lumps.Add the remaining broth.Simmer the gravy, whisking constantly, until it begins to thicken and is bubbling. This could take about 5 minutes.Reduce the heat to low, and whisk in the dried thyme, some freshly cracked black pepper, and 1 tsp of Marmite.Taste your gravy and decide whether you want to add a bit more Marmite, and adjust the seasonings as necessary.Transfer to a gravy boat, and serve hot!