Make the blueberry mix: In a small saucepan, add 3/4 cup of the blueberries, the water, and a tiny pinch of salt. Cook over medium heat for 3–5 minutes, stirring, until some berries burst and release juices.
Thicken (optional): If you prefer a thicker swirl, dissolve the cornstarch in 1 teaspoon cold water.
Stir into the berries and simmer 30–60 seconds until slightly glossy. Remove from heat and let cool 5 minutes. Stir in the remaining 1/4 cup fresh blueberries for texture.
Mix the yogurt base: In a bowl, whisk the Greek yogurt, lemon juice, lemon zest, honey, vanilla, and sea salt until smooth.
Taste and adjust sweetness or lemon as needed.
Assemble the cups: Place your silicone cups or lined muffin tin on a small tray. Spoon about 2 tablespoons of the lemon yogurt into each cup.
Add the blueberry swirl: Add a teaspoon of the blueberry mixture on top of the yogurt in each cup. Use a toothpick or knife tip to gently swirl.
Top it off: Add another tablespoon of yogurt to cover, then a small dot of blueberry on top for a pretty finish.
Chill to set: Refrigerate for at least 1–2 hours.
For a firmer, almost semifreddo-like bite, freeze for 45–60 minutes.
Serve: Garnish with a few fresh blueberries or a pinch of zest. Enjoy cold.