a find in flatbush: regina's cafe, 1824 avenue u (corner of east 19th). russian food, friendly proprieters, but most of all the potato vareniki (a kind of dumpling) with onion, and the sweet cottage cheese blintzes. were we not so full we would have tried the "crawfish for beer" and "small shrimps for beer". most expensive item on menu: shrimps in garlic white wine sauce for $9.95. what sluggo and nancy call a regular gourmet cabbie special!