Combine the ground flax meal and water in a small bowl. Let this rest for 10 minutes, stirring occasionally. This mixture creates flax eggs. Then, whisk the flax eggs together with the vegetable stock. Set aside.
Into a large saute pan or pot, melt 3/4 cups of the vegan butter over medium-high heat. Once hot, add the onion and celery in and cook for 8 minutes, stirring occasionally.
Then, add in the rosemary, thyme, sage, salt, and pepper. Stir well and cook for 1 minute.
Preheat the oven to 350 degrees Fahrenheit. Heavily grease a 9x9 inch baking dish with butter.
Now, into a large mixing bowl, toss together both of the cubed breads. Evenly pour the vegetable stock-flax egg mixture and the sauteed vegetable-herb mix over the cubed bread. Quickly but gently, stir everything together to coat the bread evenly.
Dump this mixture into the greased baking dish and spread it evenly across. Evenly dollop across the 1/4 cup of butter over the stuffing. Wrap the top of the dish in tin foil and place it on the middle oven rack to bake for 40 minutes.
Remove the tin foil and bake for 35 more minutes.
Enjoy! If not eaten immediately, I recommend keeping it covered, as it will thicken and become more firm as it cools down. Wrapping a piece of plastic wrap over the dish will trap steam over the stuffing, keeping it super moist!