Sift cocoa powder over a medium mixing bowl to remove any lumps. (I know–sifting is the worst, but you don’t want any lumps in your pudding.)
Add the maple syrup, vanilla, salt, and espresso powder, and whisk slowly to combine. The mixture will seem very dry at first but will come together eventually and resemble a thick, fudgy sauce.
Pour in a few splashes of the milk and stir gently to create a paste (this will help prevent lumps from forming). Then add the rest of the milk, and whisk until smooth. Whisk in the Greek yogurt until smooth.
Add chia seeds and whisk to combine. Cover the bowl with plastic and refrigerate overnight, or at least 4 hours, until the mixture thickens into a pudding-like consistency. I find it helps to whisk it once about 30 minutes in to make sure the chia seeds stay distributed in the mixture.
Once set, stir the pudding once more. Scoop out your desired portion, and enjoy with any toppings. You can also portion the mix into jars and store them in the refrigerator for 4 additional days.
TO STORE: Cover your chia seed pudding and place in the refrigerator for up to 4 days.
TO FREEZE: Place your chia seed pudding in small, airtight freezer-safe containers and store in the freezer for up to 2 months. Place your pudding in the refrigerator to thaw the day before you want to eat it.