In a small bowl, dissolve the espresso powder in 2 tablespoons of hot water. Stir until completely smooth and set aside to cool for 2 minutes.
In a large mixing bowl, whisk together the mascarpone cheese, maple syrup, vanilla extract, and salt until smooth and creamy with no lumps remaining.
Add the dissolved espresso mixture to the mascarpone blend and whisk until evenly combined and slightly paler in color.
Pour in the milk and stir gently until the mixture is uniform. The mascarpone may appear slightly curdled at first but will smooth out as you stir.
Add the rolled oats and fold everything together until the oats are completely coated and no dry patches remain at the bottom of the bowl.
Divide the mixture evenly among 4 mason jars or airtight containers, filling each about three-quarters full to leave room for toppings.
Cover tightly with lids and refrigerate for at least 6 hours or overnight. The oats will absorb the liquid and thicken to a creamy, spoonable consistency.
Before serving, give each jar a quick stir, then dust the top generously with unsweetened cocoa powder using a fine-mesh sieve for even coverage.
