Preheat oven to 165 degrees C. Line 24 muffin cups with patty cups. In the top of a double boiler combine the chocolate and butter. Heat, stirring occasionally, until mixture is melted and smooth. Remove from heat and allow to cool to lukewarm.
Sift flour and sugar together into a large bowl. With mixer on low speed, beat in eggs one at a time. Stir in chocolate mixture, vanilla and pecans. Fill patty cups 2/3 full.
Bake in the preheated oven for 20-25 minutes. Do not overcook. Tops should be shiny but give slightly when touched.