Preheat oven to 350°. Lightly butter miniature muffin pans (24 cups total). Place muffin pans on a baking sheet.
Whisk together flour and salt. Set aside.
In a medium saucepan over low heat, melt butter, chocolate, and brown sugar. Stir frequently to avoid overheating or burning. Remove from heat when mixture is smooth. Allow to cool for 1-2 minutes.
Stir in vanilla and egg until well-blended. Add flour and stir just until incorporated. Batter should be smooth and glossy.
Spoon batter by teaspoonfuls into muffin cups, filling each cup about 3/4 full. Batter should fill 16-24 cups. Fill any empty cups with 1 teaspoon water.
Bake 14-16 minutes, until the tops spring back when touched. Cool on wire racks for a few minutes. Then, remove from pans to cool completely on wire racks.