Preheat oven to 350 degrees F (175 degrees C). Grease 24 mini muffin cups.
Beat brown sugar, butter, eggs, and vanilla extract together in a bowl using an electric mixer until smooth and creamy. Mix flour and pecans together in a bowl; stir into creamy mixture until batter is smooth. Spoon batter into the prepared muffin cups.
Bake in the preheated oven until a toothpick inserted in the center of a muffin comes out clean, 10 to 12 minutes.
