Special equipment: eight 1-cup Mason jars with lids
Whisk together the Greek yogurt, muscovado sugar, espresso and orange zest and juice in a bowl until smooth. Cover and refrigerate for at least 2 hours and up to 24 hours.
About an hour before serving, combine the raspberries, strawberries, sugar to taste, and chopped mint in a bowl. Layer the berries, granola and yogurt mixture in eight 1-cup Mason jars. Top the jars with some more granola, then cover with lids and refrigerate for at least 1 hour. Garnish with fresh mint sprigs and serve.