In a microwave safe bowl combine the brown sugar, light corn syrup, and butter.
Microwave for 3 to 4 minutes until it starts boiling. You will want to remove the bowl from the microwave to stir the ingredients two times during this process.
Once the ingredients are boiling remove from the microwave and stir in the peanut butter until the topping is smooth.
Once the peanut butter is stirred in add the evaporated milk and stir in until combined.
Serve the peanut butter ice cream topping warm over your favorite ice cream.