Set the oven rack to the lower and upper-middle position—Preheat to 350ºF (177ºC).
Slice the bread into about ¾-inch cubes and then spread in a single layer on two large sheet pans. There should be about 16 cups of cubes.
Toast the cubes in the oven until the edges are dry and crisp, about 10 minutes, gently stirring after 5 minutes. Allow to completely cool on the sheet pan while cooking the rest of the stuffing. The bread will completely dry out.
Heat a large 12-inch skillet over medium heat. Add the olive oil, then once hot add in the onions and celery, saute until tender, 5 to 6 minutes. Add garlic, saute until fragrant, 30 seconds. Add sage, rosemary, thyme, salt, and pepper, stir and cook for 30 seconds—transfer mixture to the bowl with the bread cubes.
Add parsley and garlic powder to the bread mixture and gently stir to combine.
In a medium bowl, whisk together eggs and vegetable stock. Pour the liquid evenly over the bread, gently stir to combine. Allow soaking for 5 minutes.
Set the oven rack to the middle position—grease a 9x13-inch baking pan with cooking spray or olive oil. Evenly spread the stuffing mixture into the pan.
Cover with foil and bake for 20 minutes. Uncover and bake until the internal temperature reaches at least 144ºF (62ºC) and the surface is slightly dry, about 15 to 20 minutes. Serve the stuffing warm.
Recipe Yield: 8 cups
Serving Size: 1 cup
Using dried herbs: Use half the amount of the fresh herbs (sage, thyme, and rosemary), a total of 1 tablespoon dried.
Make-ahead: Cut and dry bread up to 5 days before using, store in an airtight container. Combine all of the stuffing ingredients, cover, refrigerate, and bake within 1 day. Bake covered for 30 minutes, then remove and continue to bake until the internal temperature reaches at least 144ºF (62ºC) and the surface is dry.
Reheating: Cool the baked stuffing, cover, and refrigerate. Warm individual portions on high power in the microwave in 30-second intervals until warm. Alternatively, heat in a 300ºF (149ºC) oven until warmed through.