Mix the butter, tonka bean zest and sugar until creamy. Stir in eggs one at a time. Mix the flour with baking powder and stir alternately with the milk into the butter mixture. Grease a Guglhupfform with butter and sprinkle with the breadcrumbs. Pour the batter into the mold.
Bake in the preheated oven at 180 ° C for about 45-50 minutes. Turn out of the mold and let cool down.
Sprinkle with powdered sugar before serving.
Tip: If you don`t like sultanas, you can simply leave them out.