Mix the brown sugar, pecans and flour in a mixing bowl. Whisk the butter, eggs and vanilla extract in a separate bowl until well blended. Combine the butter mixture into the brown sugar mixture, slowly, and stir just until moistened.
Fill paper-lined miniature muffins cups about 2/3 full. Bake at 350 degrees for about 20-22 minutes, or until a toothpick comes out clean. Serve warm.