In a medium saucepan, bring millet and 3 cups of vegetable broth to a boil. Reduce heat, cover and simmer for 30 minutes.
Meanwhile, heat butter in a large skillet over medium-high heat and cook onion for 3-4 minutes. Add garlic, thyme, sage, parsley, mushrooms, celery and Brussels sprouts and cook, stirring occasionally, for an additional 8-10 minutes, until vegetables are cooked.
Lightly whisk eggs into 3/4 cup vegetable broth and mix with cooked vegetables, millet, salt and pepper. Pour mixture into lightly greased 9×12 baking dish, and bake covered at 375º for 30 minutes.
Uncover and bake for an additional 25-30 minutes. Enjoy!