Preheat oven to 250°F In a large mixing bowl, mix the confectioners sugar into the yogurt one cup at a time with a hand blender. Using tongs or chopsticks, dip the pretzels, one at a time into the frosting and place them on the wire cooling rack. (Place a cookie sheet under the wire rack to catch the excess frosting that will drip from the pretzels.) Once all pretzels are coated, turn your oven off and place the wire rack and cookie sheet in, leaving the oven door slightly open. The excess heat will help the frosting dry without leaving the pretzels soggy. Allow frosting to harden for 3-4 hours, remove from oven, and store pretzels in an airtight container for up to 3 days.