Recipe(tried): applebee's blondies butter sauce

This is as close as i could come to matching that sauce they put on their blondies. My husband is the ultimate "Blondie's" fan, he will order one even if he is stuffed fromt his main course...
I do not have an exact amount figured up, i just put these following ingredients together until it tastes right;
take margarine (about 1/4 c.)
and then about 1/2c. surgar and mix together in a small sacue pan, then melt together. Now turn on low heat and in a measuring cut put in about a 1/2 c. of milk and about 1-2 tbs. of cornstarch blend well and add to the butter mixture then add about 1 tsp of "butter flavored extract" maybe more depending on your taste. simmer these together until blended well and thickend. You may want to add more sugar. I hope this turns out.
"Blondies Fan"