Preheat oven to 350F.
Prepare dulce de leche. Set aside.
In a mixer, beat butter and sugar, until it is light and fluffy (making sure to scrape sides frequently).
Add eggs one at a time and beat well after each addition.
Add molasses and vinegar slowly to avoid the mixture from separating. Sift together dry ingredients and add to creamed butter mixture just until combined.
Wrap dough in saran wrap and roll into a 1” diameter log and chill for at least 30 minutes. Dough can be frozen at this point or kept in the refrigerator for up to 3 days before baked. Cut off 1” pieces at a time and roll into a ball and dip into excess sugar.
Bake for about 7 to 9 minutes. Allow to cool for 20 minutes before spreading filling on bottom of one cookie and sandwiching with another.