In a small skillet, cook onions in oil until tender. Stir in spinach; cook and stir for 2 minutes longer. Cool and squeeze dry. In a large bowl, combine the cheese, dill and parsley. Stir in spinach mixture; set aside.
Place one sheet of phyllo dough on a lightly floured surface. Lightly brush with butter. Top with another sheet of phyllo dough; brush with butter. Repeat with remaining dough. (Keep remaining phyllo covered with plastic wrap and a damp towel to prevent it from drying out.) Place a 6-oz. custard cup upside down on dough. Cut around custard cup with a small pizza cutter.
Place about 4 teaspoons of cheese mixture in the center of each circle. Bring edges of circle up and around cheese, forming a tart. Brush dough with butter.
Place on an ungreased baking sheet. Bake at 350° for 25-30 minutes or until golden brown and spinach mixture is hot.
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