Prep the pan. Line an 8x8-inch (20x20 cm) pan with parchment paper, leaving overhang for easy lifting. Lightly mist with oil if you want super clean release.

Measure oats. Add 3 cups of rolled oats to a large bowl and set aside. If you like a denser bar, lightly crush a cup of the oats with your hands for a tighter texture.

Make the cocoa syrup. In a medium saucepan over medium heat, combine 6 tablespoons butter, 1/3 cup milk, 1/2 cup brown sugar, 1/3 cup honey (or maple), 1/4 cup unsweetened cocoa powder, and a pinch of salt. Stir constantly until the mixture is smooth and just starts to bubble around the edges.

Let it simmer briefly. When it reaches a gentle simmer, cook for about 60 seconds, stirring. This helps the sugar dissolve and thickens the syrup slightly. Avoid a rolling boil.

Add peanut butter and vanilla. Remove from heat. Stir in 3/4 cup creamy peanut butter and 2 teaspoons vanilla until fully melted and glossy.

Combine with oats. Pour the warm mixture over the oats. Stir well, scraping the bottom, until every oat looks coated. If adding mix-ins like nuts, coconut, or seeds, fold them in now. If using chocolate chips, let the mixture cool 3–4 minutes so they don’t melt completely.

Press into the pan. Transfer the mixture to the lined pan. Use a spatula or a flat-bottomed measuring cup to press it firmly and evenly into the corners. Firm packing helps the bars set and slice neatly.

Optional topping. Sprinkle a small handful of mini chocolate chips or flaky salt on top. Gently press so they stick.

Chill to set. Refrigerate for at least 2 hours, or until firm. For faster setting, place in the freezer for 30–40 minutes.

Slice and serve. Lift the slab out using the parchment. Cut into 12–16 bars with a sharp knife. Wipe the blade between cuts for clean edges.