Roasted Potatoes without herbs pudding

1 pound potatoes fingerling or red new potatoes, washed 1 tablespoon olive oil 1 each yellow onion halved and thinly sliced 2 cloves garlic or to taste,[...]

1 1/2 pounds potatoes peeled and cut into 1 1/4 inch chunks 3 tablespoons goose fat or duck fat, rendered, or olive oil * 1 tablespoon parsley leaves chopped,[...]