HEAT oven to 375ºF.
MIX first 4 ingredients and egg yolk until blended.
SEPARATE crescent dough into 8 triangles. Cut each triangle diagonally in half. Spoon 1 Tbsp. spinach mixture onto center of each triangle. Bring corners of dough to center over filling, overlapping ends; pinch ends together to seal. Place on baking sheets. Beat egg white lightly; brush onto bundles.
BAKE 12 to 15 min. or until golden brown.