In a large bowl, combine 1/2 cup melted salted butter, 1 cup finely chopped toasted pecans, and 1/4 cup clear or green creme de menthe. Mix with an electric mixer or a wooden spoon until evenly combined.
Gradually add 4 cups powdered sugar to the bowl, about 1 cup at a time, stirring after each addition until the mixture becomes a firm, moldable dough that holds together when pressed.
Cover the bowl with plastic wrap and refrigerate for 1 hour to firm the mixture.
Line a baking sheet with wax paper or parchment paper. Lightly dust your hands with powdered sugar.
Remove the chilled mixture from the refrigerator. Using about 1 tablespoon of mixture per truffle, shape into 1-inch balls and place them on the prepared baking sheet. Cover with plastic wrap and refrigerate for 30 minutes to firm.
Place 2 cups semi-sweet chocolate chips and 2 teaspoons shortening in a microwave-safe bowl. Microwave in 20-second intervals, stirring well between intervals, until the chocolate is completely melted and smooth.
Using a fork or dipping tool, dip one chilled truffle at a time into the melted chocolate, letting excess chocolate drip back into the bowl, then return the coated truffle to the prepared baking sheet.
Refrigerate the coated truffles until the chocolate is set (about 15–30 minutes). Store chilled until ready to serve.