Combine the Base Ingredients: In a medium mixing bowl, add the rolled oats, cooled strong coffee, milk, Greek yoghurt, maple syrup (or honey), vanilla extract, and a tiny pinch of salt. Stir everything together thoroughly until the oats are fully moistened and the mixture takes on a light brown, creamy appearance. You should see no dry spots of oats remaining.

Prepare the Mascarpone Swirl: In a separate smaller bowl, gently whisk the mascarpone cheese until it's slightly softened and smooth. It should become a pale, off-white, spreadable consistency. If it's too stiff, a quick minute at room temperature will help.

Layer the Oats: Divide half of the oat mixture evenly between two jars or serving glasses. The base layer should look like a rich, coffee-coloured foundation. If using, sprinkle a tablespoon of crushed digestive biscuits or ladyfingers over this layer for added texture; you'll hear a slight crunch as they settle.

Add the Mascarpone Layer: Carefully spoon half of the whisked mascarpone cheese over the oat layer in each jar. Gently spread it out to form a distinct, creamy white layer. It doesn't have to be perfectly smooth – a rustic swirl will look lovely.

Repeat and Chill: Add the remaining oat mixture over the mascarpone layer, followed by the remaining mascarpone cheese. You'll now have distinct, appealing layers of creamy brown oats and pale white mascarpone. Cover the jars tightly with lids or cling film and place them in the refrigerator for a minimum of 8 hours, or preferably overnight. The smell of coffee and vanilla will subtly emerge as you seal them.

Garnish and Serve: The next morning, retrieve your overnight oats from the fridge. The mixture should be thick, creamy, and wonderfully chilled, with the oats having absorbed most of the liquid. Dust generously with unsweetened cocoa powder over the top – you'll notice the fine powder creating a deep, earthy brown contrast against the light mascarpone. For an extra flourish, you could add some dark chocolate shavings. Serve immediately and enjoy the delightful aroma of coffee and chocolate.