Heat oven to 400°F. Cut four 4-inch circles from each piecrust. Place each circle in own muffin-pan cup, pressing to fit interior of cup. Place another muffin pan on top, pushing down to secure crusts. Bake 15 minutes, remove from oven, and lift top muffin pan off crusts. Lower oven temperature to 350°F.
In medium bowl, mix together sugar, spice, and salt. Whisk in eggs, squash, and half-and-half. Divide filling among baked shells and bake 30 minutes.