In a mixing bowl, mix together peanut butter, softened butter and vanilla with a mixer on low. You can easily get sticky things like peanut butter, evaporated milk, etc. out of a measuring cup if you spray it first with non-stick cooking spray like Pam.
Add the two sugars and mix until combined. Take a small baking sheet or large plate (something that will fit in your freezer) and line with waxed paper or non-stick foil. Lay out your square pretzels (or if you can't find square, the mini traditional knotted pretzels will work too) on the sheet.
Using a teaspoon measure, scoop up the peanut butter mixture and roll into balls. Place a ball on each pretzel and top with another pretzel, pushing down to form little sandwiches. Place in the freezer to firm up for 30 minutes.
Melt the dipping chocolate according to the directions and dip each pretzel sandwich halfway. Place on a non-stick sprayed cooling rack to dry, or on a sheet of waxed paper or foil. They will firm up faster if you put them in the refrigerator.
I have also taken a shortcut when making these by using Reece's Mini Peanut Butter Cups or Rolos for a caramel version, instead of the peanut butter mix, baking for 3-5 minutes at 350 until the chocolate just begins to soften before topping with the second pretzel and pressing to make the sandwiches. Then drizzle with the dipping chocolate before refrigerating to harden - cuts time in half!