Wash and pit the mirabelle plums, or drain if using jarred. Heat 100 ml apple juice and 1 tablespoon honey in a saucepan over medium-high heat until boiling. Reduce heat to medium, add the plums, and simmer for 5 minutes. Mix the cornstarch with the remaining 50 ml apple juice in a small bowl. Pour this into the saucepan and bring to a boil over medium heat, stirring constantly. Remove from heat and let cool to room temperature, about 10-15 minutes.
Grate the chocolate. Mix the quark, curd milk, remaining 1 tablespoon honey, cinnamon, and 2/3 of the grated chocolate in a bowl.
Divide the cooled plum compote among serving glasses. Top with the quark mixture and sprinkle with the remaining chocolate.