Fill a small bowl with cold milk and sprinkle the gelatin powder on top. Let the gelatin bloom for 5 minutes until it absorbs the milk and becomes a gel-like mass.
Meanwhile, in a small pot, whisk together the whipping cream, pumpkin puree, brown sugar, vanilla extract, cinnamon, nutmeg, ginger, allspice, and cloves until smooth. Bring this mixture to a simmer on low-medium heat. Once small bubbles start forming at the surface, stir in the bloomed gelatin and milk mixture until it completely dissolves.
Pour pumpkin panna cotta into serving glasses and chill in the fridge for about 30 minutes or longer until set. The texture should be firm to the touch but a little wobbly when shaken.
Notes
Vanilla Panna Cotta: Same method as the pumpkin panna cotta except without the pumpkin puree and pumpkin spices. Bloom 2 ¼ teaspoons gelatin powder in 300g milk. Heat 300g whipping cream and 2 teaspoons vanilla extract to a simmer and stir in the bloomed gelatin and milk mixture until dissolved.
To make a layered panna cotta: Fill small bowls with rice and place serving glasses in the bowls at a tilted angle (optional). Pour in your first layer of panna cotta and chill for 15-30 minutes. Turn the glass to a different angle (optional) and pour in the second layer and chill again. Repeat and alternate the pumpkin and vanilla layers until you're happy with the look.