Wash, halve and stone the plums. Cut the halves into small pieces. Mix butter and sugar with the whisk of the hand mixer. Stir in egg. Add buttermilk slowly and stir until smooth. Mix flour, baking powder, baking soda and almonds and add.
Finally fold in the plums. Line the hollows of a muffin tray (12 hollows) with paper sleeves. Fill in the dough evenly. Bake the muffins in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for 20-30 minutes. Remove the muffins from the trays and let them cool on a cake rack. Mix sour cream, lemon juice and vanilla sugar and serve with the muffins
1 hour waiting time