For each cup, start with one sheet each of glassine and parchment paper. Cut whichever sheet will form the inside of the cup to 9 1/2 inches square; cut the other to 10 inches square. Center the small sheet on top of the large sheet, and attach in center with a piece of double-sided tape.
Fold square in half to form a triangle.
Fold bottom-right corner to left side.
Fold bottom-left corner to right side.
Fold front top points over front of cup, then rear top points behind back. To complete, hold top of cup open with one hand, then gently press bottom seam up at the center with other hand.
Images and directions are from Martha Stewart.