In a medium saucepan over medium heat, combine 1 cup (240 ml) of the heavy cream and the almond milk.
Bring the mixture to a gentle boil, then reduce the heat to low and let it simmer for about 1 hour, or until it has reduced slightly and thickened.
Remove the saucepan from the heat.
Add the stevia and butter, whisking until the butter is fully melted and the mixture is smooth.
Sprinkle in the xanthan gum, instant coffee, and vanilla extract.
Whisk vigorously until the coffee is completely dissolved and no lumps remain.
Set aside to cool completely to room temperature.
In a separate large bowl, use a hand mixer or stand mixer to whip the remaining 1 ½ cups (360 ml / 12.2 fl oz) of heavy cream until stiff peaks form.
Gently fold the cooled coffee mixture into the whipped cream until just combined, being careful not to overmix.
Pour the final mixture into a loaf pan or other freezer-safe container.
Cover and freeze for at least 6 hours, or until firm.
Let it sit at room temperature for 5-10 minutes before scooping for the best texture.
