Austrian Germknoedel: Steamed Sweet Jam-Filled Dumplings

Name: Austrian Germknoedel: Steamed Sweet Jam-Filled Dumplings
Cuisine: European
Ingredients: 1 package instant yeast (2 1/4 teaspoon); 3 3/4 cups all-purpose flour; 1/2 cup sugar; 1 teaspoon lemon zest; 2 tablespoons vanilla sugar or sugar plus 1/2 teaspoon vanilla extract; 1/2 teaspoon salt; 1 egg; 5 tablespoons butter, softened; 1 cup lukewarm milk; 3/4 cup powidl or plum jam; you can substitute cherries or Nutella; 1 tablespoon rum (optional); 1/4 teaspoon cinnamon (optional); 1/3 cup poppy seeds; 1/3 cup sugar; Melted butter