I made it a little while ago and it is v. tasty.
Blend in blender until nearly smooth:
1/2 of tart green apple (cored, peeled & chopped up)
1 shallot (peeled & cut up)
3 T apple cider vinegar
1 1/2 tsps sugar
1/8 tsp kosher salt
1/8 tsp pepper
With blender running, gradually add 1/4 cup walnut oil in thin steady stream.
Makes 3/4 cup & can be prepared several days in advance.
I do not like apple cider vinegar and so I used a champagne vinegar instead. Still had a nice apple/tart taste. Recipe calls for using this on a beet & goat cheese sald with spiced pecans. I'm doing endive, walnuts & goat cheese (or maybe blue ...).