Finely chop half of the Cremini mushrooms and transfer to a medium bowl with the ground chicken, breadcrumbs, Pecorino, egg, 1 clove of the minced garlic, parsley, 1 teaspoon kosher salt and black pepper, to taste.
Gently shape into 25 small meatballs, bake 15 to 18 minutes, until golden.
In a small bowl whisk the flour with the Marsala wine and broth.
Heat a large skillet on medium heat.
Add the butter, garlic and shallots and cook until soft and golden, about 2 minutes.
Add the mushrooms, season with 1/8 teaspoon salt and a pinch of black pepper, and cook, stirring occasionally, until golden, about 5 minutes.
Return the meatballs to the pot, pour the Marsala wine mixture over the meatballs, cover and cook 10 minutes.