Add the boiling water to a medium bowl and whisk in the sugar-free Jell-O mix until fully dissolved, making sure no granules remain.

Stir in half of the Greek yogurt, whisking gently until smooth and well blended.

Add the remaining yogurt and whisk until creamy and lump-free, with a thick but pourable consistency.

Stir in the vanilla extract if using, especially for citrus flavors to add a soft, creamy note.

Pour the mixture evenly into small bowls or glasses and cover with plastic wrap.

Refrigerate for 1–2 hours until set; the texture should be firm yet slightly springy.

Serve chilled, topped with whipped cream, fresh fruit, or a bit of zest if desired.