Cut the spring onions into thin slices, separating the white parts from the green parts. Grate the cheese. Set the spring onions and cheese aside.
Heat some butter in a large pan over medium heat. Add the white parts of the spring onions and cook gently for 3-4 minutes until softened, without browning.
Add the spaetzle and stir for 2-3 minutes to heat through.
Reduce the heat to medium-low. Add roughly 1-2 handfuls of grated cheese and some milk. Mix well, cover with a lid, and cook for 2-3 minutes until the cheese melts. Stir well.
Repeat step 4 with the remaining cheese and milk in batches, stirring well between additions, until all ingredients are incorporated (about 2-3 more times).
Stir in the green parts of the spring onions and freshly ground pepper to taste. Mix well and serve immediately.