Bloom the gelatin. Add 3 tablespoons of cold milk to a small bowl.
Sprinkle the gelatin evenly over the surface. Let it sit for 5–10 minutes until it looks swelled and slightly translucent. This step prevents clumps.
Warm the dairy. In a medium saucepan, add the heavy cream, remaining milk, sweetener, and salt.
If using a vanilla bean, add the seeds and pod now. Heat over medium, stirring, until the mixture is steamy and the sweetener is dissolved. Do not let it boil.
Add vanilla and gelatin. Remove the pan from heat.
Stir in the bloomed gelatin until fully dissolved; this takes about 1 minute. If using extract instead of a bean, add it now. Taste and adjust sweetness, keeping in mind the flavor will soften slightly once chilled.
Strain for silkiness. For the smoothest texture, pour the mixture through a fine-mesh strainer into a large measuring cup with a pour spout.
This removes any undissolved bits or vanilla pod remnants.
Portion and chill. Divide the mixture into 6 small ramekins or glasses. Let them cool on the counter for 15 minutes, then cover loosely and refrigerate at least 4 hours, or until set with a gentle wobble. Overnight is even better.
Serve. Enjoy straight from the cups, or unmold by dipping each ramekin briefly in warm water and running a thin knife around the edge.
Top with berries or your favorite sugar-free garnish.