Preheat oven to 375°F Lightly Butter nonstick muffin pan or line with paper baking cups.
In large bowl, whisk egg. Whisk in brown sugar, Milk, Butter, corn syrup and vanilla. Sprinkle with flour, baking powder and salt and whisk until blended and smooth.
Spoon into prepared muffin pan. Bake for 15 to 20 min or until cake tester inserted into centre cupcake comes out clean.
Let cool in pan on rack for 10 minute Transfer to rack to cool completely.
Icing: In bowl, using electric mixer, beat 2 tbsp of the butterscotch sauce with Butter until blended. Sift icing sugar into bowl and beat until smooth, adding as much of remaining butterscotch a little at a time as necessary to make icing smooth and spreadable. Spread over cooled cupcakes.
Tips: If you don't have dark brown sugar, use light brown sugar and add 2 tsp (10 mL) fancy molasses.