In a heavy bottomed saucepan, combine water and allulose.
Set up a candy thermometer, if using. Set the saucepan over low heat and allow to cook to soft ball stage or 240°F.
Meantime, while the syrup is cooking, combing egg yolks and vanilla paste in a bowl.
Using a wire whisk, whip on high until light and doubled in volume, approximately 8 minutes.
When the syrup reaches 240°F, remove from heat. Reduce mixer speed to low. In a slow, even stream, away from the whisk, gently pour in the syrup. Continue until all the syrup has been added.
Transfer to another container and let cool. Note that this may be made ahead of time. To store, refrigerate in an airtight container.