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1
Combine the half-and-half and heavy cream in a medium saucepan and bring to a simmer over medium heat, stirring occasionally.
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2
Remove from the heat and set aside.
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3
Whisk the egg yolks in a large mixing bowl until they lighten in color.
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4
Gradually whisk the sugar into the yolks until smooth.
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5
Slowly ladle one-third of the hot dairy into the yolk mixture, whisking constantly.
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6
Return this mixture to the pot containing the rest of the dairy.
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7
Cook over low heat, stirring frequently, until the custard thickens slightly, enough to coat the back of a spoon and reaches 170 to 175 degrees F.
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8
Wash the original mixing bowl.
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9
When the custard is ready, transfer to the bowl, whisk in the coffee liqueur, espresso powder and vanilla, and cool at room temperature for 30 minutes.
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10
Cover and refrigerate until the temperature drops below 40 degrees F, 3 to 4 hours.
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11
Liquid nitrogen procedure: Pour the ice cream base into the bowl of a stand mixer fitted with the paddle attachment.
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12
Turn the speed to low.
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13
With the mixer running, slowly pour in the liquid nitrogen while counting to ten.
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14
Increase the speed to medium and mix for 1 minute.
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15
Serve immediately or store in freezer.
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16
Ice cream maker procedure: Pour into a prepped ice cream maker and process according to the manufacturer's directions.
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17
Within 25 to 30 minutes the ice cream will attain a classic soft-serve consistency.
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18
Serve as is for soft serve or freeze for another 3 to 4 hours to allow the ice cream to harden.
