NOTE: You have to make the homemade caramel first. Don't cheat and try to use packaged caramels - it won't be same.
Grease an 8 x 8 inch square pan.
In a heavy 4 quart saucepan melt butter over medium heat. Add brown sugar, corn syrup and milk. Stirring constantly, heat to 248 to 250 degrees F (116 to 120 degrees C). *You will need to use a candy thermometer to monitor the temperature. You should expect to be stirring constantly for 45 minutes. Be patient. You can't rush this process.
Remove from heat and stir in vanilla extract. Pour into prepared pan. Let sit out on the counter until it is room temperature - or a solid state.
When caramel has cooled and set -chill in refrigerator until firm. (At least an hour or two!)
Combine the dark and semi-sweet chocolate and melt it in the top of a double boiler or in a bowl in the microwave. Stir until smooth.
Once caramel is ready - remove from refrigerator and cut into small cubes to fit on a pretzel. NOTE: Cut the caramel as you go because it will start to melt.
Place a caramel cube on a pretzel.
Use two forks to carefully dip the pretzel/caramel into the bowl of chocolate to cover completely.
Place on wax paper to cool.