MIX TOGETHER THE BROWN SUGAR WITH THE MELTED BUTTER IN A BOWL UNTIL WELL BLENDED. ADD PECANS AND FLOUR MIXING WELL TO COMBINE. TRANSFER FILLING TO WAXED PAPER IN A JELLYROLL BAKING PAN AND SHAPE INTO A 7" SQUARE. CUT INTO 36 ( 1 1/4" PIECES. REFRIGERATE 1 HOUR OR OVERNIGHT.
COMBINE BUTTER, SUGARS AND EGG YOLK IN A MEDIUM BOWL. ADD REMAINING INGREDIENTS MIXING WELL TO INCORPORATE. COVER AND REFRIGERATE 4 HOURS OR TILL FIRM. ROLL HALF OF THE DOUGH ON A WELL FLOURED SHEET OF WAXED PAPER TO 12" SQUARE. REPEAT WITH SECOND HALF OF DOUGH. ( IF DOUGH BECOMES SOFT, REFRIGERATE 1 HOUR).
LIGHTLY SCORE 1 LAYER OF DOUGH AT 2" INTERAVALS TO FORM 36 SQUARES. PLACE 1 SQUARE OF FILLING IN CENTER OF EACH DOUGH SQUARE. CAREFULLY PLACE SECOND LAYER OF DOUGH OVER FILLING. PRESS GENTLY BETWEEN ROWS AND CUT WITH A PIZZA CUTTER OR A SHARP KNIFE. TRANSFER TO UNGREASED COOKIE SHEETS AND BAKE 14 TO 16 MINUTES OR UTNIL LIGHTLY BROWNED.
REMOVE FROM OVEN AND COOL ON SHEETS 5 MINUTES. REMOVE TO A WIRE RACK AND COOL COMPLETELY. DRIZZLE TOPS OF COOKIES WITH SOME MELTED CHOCOLATE IF YOU LIKE.
NOTE: YOU CAN SUBSTITUTE 1" SQUARES OF CHOCOLATE FOR THE BROWN SUGAR FILLING.