In large bowl, sift together flour, cocoa, sugar, baking powder, salt, and baking soda. In medium bowl, whisk eggs, melted butter, and milk. Pour liquid ingredients into dry and gently mix until batter is just moistened (there will be some lumps).

Melt a small piece of butter in a large non-stick skillet over medium heat. Drop 2 heaping tablespoon of batter in a hot skillet and spread into 2 1/2 inch discs. Space discs 2 inches apart. Cook until bubbles form over the entire top, about 30 seconds. Using a heatproof, non-stick spatula, carefully flip the pancake and continue to cook until done, 15 to 30 seconds more.

In small saucepan, heat milk to just simmering. Add chocolate and whisk until smooth. Whisk in vanilla. Serve over pancakes.