In a mixing bowl with a spout, mix together the allulose, xanthan gum, sugar, salt, milk powder and cocoa powder until evenly blended. It's important to mix xanthan gum with dry ingredients to help keep it from lumping. Add the syrups, eggs and ½ cup of the milk and Stir or whisk until smooth and thick.
Pour remaining 2 cups of milk and the ½ cup cream in a saucepan and heat until mixture begins to simmer.
Gradually whisk the hot milk mixture into the egg mixture to temper, then pour it all back into the saucepan.
Stir constantly (I use a heavy duty heat proof rubber scraper) over medium-low heat until mixture is 180 degrees F. This should only take a few minutes. It will start to look foamy and stick to the sides of the pot. Don't let it boil over.
Strain the mixture into a clean bowl and add the chocolate. Whisk or stir to melt the chocolate, then stir in the vanilla bean paste.
Pour the custard into a heavy duty freezer bag and submerge in ice water for about 30 minutes to quick cool. At this point it will be pretty cold and you could probably just go ahead and churn it, but I usually recommend letting it chill for at least 2 more hours.
When the ice cream is very cold, add 1 tablespoon of vodka to the freezer bag. Close it and shake it up a little just to mix. Note: There's no reason I know of that you can't add the vodka earlier in the process, I am just in the habit of adding it last and that's the way I've been making it.
Pour the mixture from the bag to the ice cream maker and churn as manufacturer directs until mixture is soft serve/frozen.
Scrape into pints. Freeze until firm (overnight). The ice cream should still be quite scoopable on day 2.
Notes
The nutrition macros are estimates based on total calories and weight of the finished batch. The full recipe comes out to about 1600 calories and 1137 grams, which works out to roughly 1.4 calories per gram. A generous scoop, measured after the ice cream has fully frozen (day 2 ), weighs about 112 to 114 grams, so that's around a half cup if you are eyeballing it. A scale is a better way to measure ice cream.