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Freeze the work bowl of an ice cream maker according to the manufacturer's instructions.
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Combine the pumpkin purée, milk, cream, spices, salt, vanilla, and pumpkin flavor in a saucepan. Set the pan over medium heat, and bring the mixture just to a boil. Remove it from the heat.
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Beat together the egg yolks, sugars, and xanthan gum until light and airy.
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Pour half the warm pumpkin mixture slowly into the egg yolk mixture, stirring constantly.
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Pour the yolk/pumpkin mixture back into the saucepan with the remaining pumpkin mixture. Cook over low heat, stirring with a heatproof spatula, until the custard thickens significantly; it will register between 170°F and 180°F on a digital thermometer.
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Remove the pan from the heat, and let the custard cool to room temperature, stirring occasionally to prevent a skin from forming. Refrigerate for at least 2 hours, or overnight.
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Transfer the custard to an ice cream maker. Freeze according to the manufacturer's instructions, adding bourbon at the end of the freezing process.
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Serve immediately if you prefer soft, creamy ice cream. For firmer consistency, transfer the ice cream to an airtight container and freeze for about 2 hours.