Heat oil in a pan over medium-high heat. Add shallot to pan and cook for about 8 minutes until softened. Add rosemary, salt, and mushrooms. Cook, while stirring occasionally, for about 8 to 10 minutes, until mushrooms have browned. Add wine and cook for a minute or so or until liquid almost evaporates. Pour in vegetable broth and simmer until reduced to about 2 cups, about 12 to 15 minutes. Combine flour, nutritional yeast, tamari, and water in a bowl, stirring until smooth. Add to pan and return to boil. Reduce heat and simmer 2 minutes or until slightly thickened. Remove from heat. Stir in vegan butter. Thin with a little water or broth to desired consistency. Finish with freshly ground black pepper.