- Preheat an oven to 300°F. Have a pot of boiling water ready.
- Pour the cream into a small saucepan and whisk in the cinnamon, allspice, ginger and nutmeg. Set over medium-low heat and warm the cream mixture until bubbles form around the edges of the pan and steam begins to rise from the surface, about 3 minutes. Remove from the heat and let stand for 15 minutes.
- In a large bowl, whisk together the egg yolks, vanilla, salt, pumpkin puree, the 1/3 cup granulated sugar and the brown sugar until smooth and blended. Slowly pour in the cream mixture, stirring until blended. Pour the mixture through a fine-mesh sieve set over a bowl. Divide the mixture among four 8-fluid-ounce-ramekins and place in a large baking pan. Add boiling water to fill the pan halfway up the sides of the ramekins. Cover the pan loosely with aluminum foil and bake until the custards are just set around the edges, about 30 minutes.
- Transfer the ramekins to a wire rack and let cool to room temperature. Cover with plastic wrap and refrigerate for at least 4 hours or up to 3 days.
- Just before serving, sprinkle 1 teaspoon granulated sugar evenly over the surface of each custard. Using a kitchen torch according to the manufacturer's instructions, move the flame continuously in small circles over the surface until the sugar melts and lightly browns. Serve immediately. Serves 4.