Heat the oven to 325 F (160 C). Bring a kettle of water to a boil.
Make the caramel: heat the allulose and water in a small heavy saucepan over medium-low heat, swirling the pan but not stirring, until it turns a deep amber, 6 to 10 minutes. Immediately pour into an 8-inch ring mold or round cake pan and tilt to coat the bottom and part of the sides.
Blend the eggs, cream, almond milk, allulose and vanilla in a blender for 30 seconds. Let it stand for 5 minutes so the foam settles, then pour through a sieve into the mold.
Cover with foil and set in a roasting pan. Pour boiling water into the roasting pan to come halfway up the sides of the mold.
Bake for 60 to 70 minutes, until the edges are set and the center jiggles slightly. Cool, then refrigerate for at least 4 hours or overnight.
Run a thin knife around the edges, place a rimmed plate on top and flip quickly. Let the caramel run down the sides.