Combine flour, cardamom and salt in bowl. Beat butter and sugar in large bowl until creamy. Beat in egg and vanilla until fluffy. Stir in flour mixture. Divide dough into thirds; flatten. Wrap in plastic. Refrigerate 1 hour.
Combine nuts, apricot preserves, cinnamon and sugar in small bowl.
Heat oven to 325 degrees F. Grease 2 large baking sheets.
On floured surface with floured rolling pin, roll third of dough into 9-inch square. Keep unused dough refrigerated. Cut dough into nine 3-inch squares. Place squares, 1 inch apart, on prepared sheets. With small knife, cut four 1-3/4-inch-long slits into each square, from each corner almost to center. Spoon 1 teaspoon filling onto center of each square; brush edges with egg white.
Fold every other corner or tip over filling to center; press lightly to stick. Place 1/4 teaspoon filling in center of each cookie. Brush tops with egg white; sprinkle with colored sugars. Repeat with remaining dough and filling.
Bake in 325 degree F oven for 12 minutes or until lightly golden. Cool cookies on wire racks. Store at room temperature or freeze. Makes 27 cookies.