Unroll refrigerated piecrust onto a parchment paper-lined baking sheet; prick piecrust all over with a fork. Spray with cooking spray. Bake in 400°F oven until crisp, about 15 minutes. Let cool, and then break into large pieces; set aside. Beat cold heavy cream and sugar in a cold bowl with an electric mixer until stiff peaks form, about 1 minute; set aside. Process ice cream, milk, instant cocoa mix, 1/3 cup toasted pecans, syrup, and salt in a blender until smooth. Drizzle the insides of 4 glasses with chocolate sauce. Pour frozen hot chocolate mixture into prepared glasses. Top with whipped cream, piecrust pieces, and additional toasted pecans.