Brown Sugar Frosting

My friend SL posted this on her blog.  Its a favorite last minute go to icing for me.  I used it twice this summer alone when we had last minute company.  I topped a boxed cake mix (with a couple of added ingredients) with this amazing yumminess....

1/2 Cup Butter
1 Cup Brown Sugar
4 Tbsp Milk
2 Cups Icing Sugar
2 tsp. Vanilla

• Put butter & brown sugar in a bowl.  Cook for 2 minutes 
• Add milk and stir
• Microwave again for 2-3 minutes.  It should be boiling now. 
• Add the icing sugar and vanilla and whisk until everything has been incorporated and you no longer see the sugar.
• Resist the urge to stick your finger in the bowl for a taste...if you do, I will be sorry, IT'S HOT!
• Cool for a bit and then pour over cake.  Let it set for a bit.