In a bowl, whisk eggs & milk. Add flour & whisk until incorporated. Whisk in parmesan cheese, sliced scallions, parsley, thyme, salt & pepper. Set aside.
Filling
Heat oil in a skillet. Add onions & sauté until translucent. Add zucchini & sauté for 3-5 minutes until zucchini is tender. Season with salt & pepper. Transfer to a bowl. Add another 2 teaspoons of oil to skillet. Add mushrooms & sauté for 5-7 minutes. Cook until mushrooms are tender & most of the moisture has cooked off. Season with salt & pepper; transfer to another bowl. Keep filling ingredients warm will you bake the Dutch Baby pancake,
Add 1 tsp of oil to skillet. Add sliced chicken sausage. Cook until browned. Transfer to another bowl. Add vegetable broth to skillet; whisk in flour & seasoning. Bring to a simmer while whisking until mixture thickens. Remove from heat & keep warm.
Bake /Serve
Preheat oven to 425 F.
Melt 4 Tbsp butter in a 10-inch cast iron skillet over medium heat. Once the butter is melted & the skillet is hot, pour in the batter. Carefully transfer the skillet to preheated oven & bake 25 minutes, The Dutch Baby will puff up during cooking, but once it’s removed from the oven & starts to cool it will deflate slightly.
When Dutch Baby is cooked, remove from oven & place some of the chicken sausage in it then top with the veggies & the remainder of chicken sausage. Ladle sauce over top & sprinkle with grated cheese & fresh thyme. Serve immediately.