Dissolve yeast in warm water. Set aside. Combine flour, half cup sugar, baking powder and salt. Stir in milk, 5 tbs melted butter, vanilla and yeast. Shape dough into a rectangle about 1 cm thick on a buttered cookie sheet. Cover dough with plum wedges. Brush plums with remaining tbs of melted butter. Combine quarter cup sugar and cardamom. Sprinkle over top of cake. Bake at 190ÂșC 30 to 40 min, or until center tests done.