CREAM THE BUTTER AND SUGAR TOGETHER TILL FLUFFY. BEAT EGG YOLKS WELL AND ADD ONE AT A TIME, STIRRING AFTER EACH ADDITION. STIR IN THE EXTRACT AND PINEAPPLE. BEAT EGG WHITES UNTIL STIFF AND FOLD INTO MIXTURE ALONG WITH THE SOUR CREAM. LINE LOAF PAN OR SPRINGFORM PAN WITH LADY FINGERS. PLACE THEM AROUND SIDES OF PAN AS WELL AS THE BOTTOM. MOUND IN half OF THE PINEAPPLE MIXTURE. TOP WITH MORE LADY FINGERS AND PILE IN THE REST OF THE PINEAPPLE MIXTURE CHILL WELL BEFORE SERVING. GOOD FOR MAKE AHEAD DESSERT, IT WILL KEEP TWO OR THREE DAYS IN REFRIGERATOR.