Place bread cubes into a large bowl. Heat milk until it starts to bubble at the edges, then pour it over bread cubes. Stir briefly to coat bread. Let soak for 15 minutes.

Melt butter in a skillet over medium heat. Add onions; cook and stir until tender. Stir in parsley, and remove the skillet from the heat.

Mix butter into the bowl with bread along with eggs, salt, and pepper. Using your hands, squeeze the dough through your fingers until it is smooth and sticky.

Bring a large pot of lightly salted water to a boil. Make a test dumpling to ensure the texture is correct. Adjust dough if needed by adding bread crumbs.