Cook spaetzle according to package directions, adding sliced carrots for the last 10 minutes.

Slice pork tenderloin in half lengthwise, then crosswise into 1/4 to 1/2-inch thick slices.

Place pork slices in a plastic bag with flour, 1/4 teaspoon pepper, and 1/4 teaspoon salt; seal and shake to coat evenly.

Heat butter in a large saucepan over medium-high heat.

Working in batches, add pork slices and cook until no longer pink, about 5 minutes, turning over.

Add frozen green beans (breaking them apart) and onions; cook, stirring, for 4 minutes.

In a bowl, whisk together sour cream, mustard, milk, dill, remaining 1/2 teaspoon pepper, and remaining 1/4 teaspoon salt.

Add sour cream mixture to the pork and vegetable mixture in the saucepan, stirring constantly.

Reduce heat to medium and cook uncovered for 5 minutes, or until vegetables are tender and the sauce is thick and creamy.

Drain spaetzle-carrot mixture.

Arrange spaetzle-carrot mixture on a platter.

Top with pork-vegetable mixture.

Serve immediately.