Line a rimmed baking sheet with parchment paper; set aside.
Put the pretzel pieces into a resealable plastic bag and crush into very small crumbs (a rolling pin or mallet works great for this).
In a small bowl, stir together the Nutella, butter, brown sugar and salt. Mix until all of the ingredients are completely blended and smooth. Add the pretzel bits to the Nutella mixture and mix thoroughly. Add the powdered sugar and mix until completely combined.
Using a small cookie scoop, or about 2 teaspoons worth of Nutella mixture, gently shape into a ball. Place the ball on the parchment-lined baking sheet and repeat with the remaining Nutella mixture. Place the baking sheet into the refrigerator and chill for at least 30 minutes.
When ready to dip the truffles, microwave the chocolate chips and vegetable shortening together in a small 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 the 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 all of the remaining truffles. Garnish with additional crushed pretzels, if desired.
Return the baking sheet to the refrigerator and again chill for at least 30 minutes. Store in an airtight container in the refrigerator for up to 1 month.