In a jar or bowl (a 14-ounce working jar or 1-pint mason jar is perfect), combine the muesli (or old-fashioned oats and cinnamon), chia seeds and nut butter. Add a splash of the milk and mix the nut butter into the oats. Then add the rest of the milk and stir to combine. Top with your fruit of choice. (If you used more milk than 1/2 cup and you want your fruit to stay on top, wait to top the oats until you're ready to serve. If you're using fruit that doesn't store well, like sliced apple or banana, wait to top the oats until you're ready to serve.) Place the lid on the jar and refrigerate overnight, or up to 5 days. When you're ready to serve, add a drizzle of maple syrup or honey if you'd like, and enjoy chilled.