Position 1 oven rack at lowest position and the other 6-8 inches above. Heat oven to 350°F.
In small bowl, combine cinnamon and sugar; mix well. In small skillet over medium heat, melt 2 teaspoons butter to cover skillet surface. Place one tortilla in pan; coat bottom side completely with butter. Place warm tortilla, butter side up, on large cutting board; sprinkle with cinnamon sugar mixture. Repeat with remaining tortillas, melting additional butter as needed.
Place baking sheet on lower oven rack. Position tortillas, cinnamon sugar side up, over two bars of upper oven rack so hanging sides are even to form an inverted taco shell. Bake 7-9 minutes or until golden. Carefully remove shells and baking sheet from oven; place tortillas on rack to cool. When ready to serve, fill each with ice cream. Top with whipped cream and sundae toppings; serve immediately.