Put the buttermilk, yoghurt, oat flakes and honey in a bowl and stir until smooth using a hand mixer. Sort the raspberries, wash and pat dry. Wash the peaches, dry them, cut them in half and remove the stone. Dice the peach halves.
Divide the buttermilk mixture into 4 bowls and spread the raspberries and peaches over them. Wash the mint, shake dry and pluck the leaves from the stems. Garnish the cold bowl with the mint leaves and serve.