Line a rimmed baking sheet with parchment paper; set aside. Place pretzel pieces into a resealable plastic bag and crush into very small crumbs with a rolling pin or mallet. In a small bowl, stir together Nutella, butter, brown sugar, and salt. Mix until all of ingredients are completely blended and smooth. Add pretzel bits to Nutella mixture and mix thoroughly. Add powdered sugar and mix until completely combined.

Using a small cookie scoop, gently shape into a ball. Place on baking sheet and repeat with remaining Nutella mixture. Place baking sheet into refrigerator and chill at least 30 minutes. When ready to dip the truffles, microwave chocolate chips and shortening in a bowl at 50% power in 30-second increments, stirring after each, until completely melted and smooth.

Working one at a time, dip one truffle into melted chocolate and use a fork to roll it around, ensuring that it is completely coated with chocolate. Let any extra chocolate drip off and place back on the parchment-lined sheet. Repeat with remaining truffles. Garnish with additional crushed pretzels, if desired. Return baking sheet to the refrigerator and again chill for at least 30 minutes. Store in an airtight container in refrigerator for up to 1 month.