Make the raspberry layer. In a small bowl, lightly mash the raspberries with a fork. Add a squeeze of lemon and a touch of sweetener if your berries are very tart. You want a chunky sauce, not a puree.

Mix the chia base. In a medium bowl or large measuring cup, whisk together milk, yogurt (if using), vanilla, sweetener, and a pinch of salt. Taste and adjust sweetness. Aim for lightly sweet; the raspberries will do the rest.

Add chia seeds and whisk well. Sprinkle chia seeds over the liquid and whisk for a good 30–45 seconds to distribute them evenly. This helps prevent clumps.

Let it sit, then whisk again. Rest the mixture for 10 minutes, then whisk again to break up any settling clumps. The mixture should begin to thicken slightly.

Layer the cups. Spoon a layer of mashed raspberries into the bottom of each cup or jar. Pour or spoon the chia mixture over the berries, leaving some headspace for toppings later.

Chill to set. Cover and refrigerate for at least 2–3 hours, though overnight is best for full thickness and flavor mingling.

Finish and serve. Before serving, top with more raspberries and your favorite add-ons: a sprinkle of granola, chopped almonds, coconut, or cacao nibs for crunch.