This is a recipe I got when working in Kansas City, Kansas, a center for Croatian immigration long ago.
Dressing:
five T oil (I use Smart Balance brand) 3 T lemon juice. You could try vinegar, but I don't like it. 1/2 to 1 tsp dried leaf thyme black pepper
Whisk all that together.
Add: chopped red onion (abt 1/2 cup) and chopped green onion (3 or 4 of them), to taste.
Boil red potatoes in their jackets. Maybe 6 of them. Use your judgment as to how many.
When the potatoes are cool enough to handle, chop them, remove some of the peel if you wish, and gently mix in the dressing with the onions in it. Refrigerate till ready to serve.
Don't let the potatoes get stone cold before mixing. Their texture won't be nice.
--------- I have read that adding a mere 1/2 tsp mayonnaise to the dressing will make it blend better. It does seem to help.