Measure and combine the dry base: In a medium mixing bowl or two individual 12–16 oz (350–475 ml) jars, combine the rolled oats (1 cup for 2 servings), chia seeds (2 tbsp), ground cinnamon (1/4 tsp), and a pinch of fine sea salt. Whisking or stirring the dry mix first helps distribute the chia and cinnamon evenly so each spoonful will have balanced flavor and texture.

Sweeten and aromatize the milk: In a separate small bowl or measuring cup, stir the unsweetened almond milk (1 1/2 cups) with the maple syrup (2 tsp) and vanilla extract (1/4 tsp). Dissolving the sweetener into the milk ensures it’s evenly distributed and the vanilla infuses the whole mixture rather than sitting in clumps.

Combine liquids and dry ingredients: Pour the sweetened almond milk over the oat–chia mixture and stir thoroughly (about 20–30 seconds) to incorporate. Pressing the oats down slightly and stirring helps the chia seeds begin hydrating uniformly; chia seeds absorb liquid and swell to form a gel that thickens the oats overnight.

Macerate half the berries: Place about half the mixed berries (approximately 3/4 cup / 112 g) in a small bowl with 1 teaspoon of the maple syrup (from the total) and a tiny pinch of cinnamon. Gently crush with the back of a spoon for 10–20 seconds until they release a little juice. This maceration step builds a compact, jammy layer of flavor and natural fruit sweetness that permeates the oats when layered.

Layer or stir in berries: For a pretty, restaurant-style presentation, spoon a thin layer of the macerated berries into the bottom of each jar, divide the oat–chia mixture between jars, then top with the remaining fresh berries (about 1/4 cup / 37 g per jar). Layering gives a striking visual contrast and provides pockets of fresh brightness against the creamier oat base. Alternatively, stir all the berries into the oats if you prefer a uniformly fruity oat.

Refrigerate to hydrate: Cover jars or bowl with lids or cling film and refrigerate upright for at least 6 hours, ideally 6–8 hours or overnight. Chilling allows the oats to absorb liquid and soften, while chia forms a gel that thickens the mixture and yields a custardy, spoonable texture—this is the key step that transforms dry oats into overnight oats.

Check texture and adjust before serving: After refrigeration, open and stir. If the mixture is thicker than you like, stir in 1–2 tablespoons of almond milk to loosen. If it’s too loose, add 1 teaspoon of chia, stir, and wait 10–15 minutes. Texture preference varies; adjust with small amounts of liquid or seeds for a perfect mouthfeel.

Plate and finish like a restaurant: Spoon into bowls or serve in the jars. Add a dollop of Greek or coconut yogurt if using (adds creaminess and tang), a drizzle of maple syrup if you prefer sweeter, and a sprinkle of toasted sliced almonds or a small handful of granola for crunch. Finish with a few whole berries and a light dusting of cinnamon for an elevated look and aroma.