Bloom the gelatin. Place cold water in small saucepan and sprinkle the gelatin over. Let sit while you gather your containers and other ingredients.
Gather your containers. Set out four small containers that can hold at least 3/4 cup of liquid. Canning jars, tea cups, drinking glasses, and ramekins are all excellent options.
Whisk pumpkin and spice mixtures. Place the cream, pumpkin, milk, maple syrup, vanilla extract, and spices into a heavy-bottomed saucepan with a pourable rim and whisk just until smooth. Heat gently over medium-low heat, whisking, just until slightly warm. Remove from heat and whisk in vanilla. Let sit off heat until gelatin mixture is ready.
Dissolve gelatin. Heat the gelatin-water mixture over low heat just until the gelatin is completely dissolved, 2-3 minutes. (Test the mixture by rubbing a small amount between your thumb and forefinger. You will no longer feel any granules when the gelatin is fully dissolved.)
Blend gelatin into pumpkin mixture. Drizzle the gelatin slowly into the pumpkin mixture, whisking constantly. Whisk until smooth.
Pour and chill. Divide the mixture evenly between the containers and set them in the refrigerator to chill. Let them sit for at least two hours, preferably overnight. The panna cottas can be made up to two days in advance.
Serve. Serve the panna cottas as they are, or top with any optional toppings, such as whipped cream, chopped pecans, graham cracker crumbs, or granola.