Combine flours, baking powder, salt; set aside. Melt chocolate chips over low heat in microwave or in a small nonstick saucepan.
In large mixing bowl, beat sour cream and canola oil with sugar and sugar substitute. Add chocolate mixture and vanilla and beat to blend. Add egg and egg substitute and beat until smooth. Add flour mixture and beat only until blended.
Split dough into fourths and wrap each fourth in plastic wrap. Freeze until firm (about 20 minutes.)
Preheat oven to 350°F. Shape each portion of dough into about 10 (1-inch) balls, and place on cookie sheets that have been coated with canola cooking spray. Bake for 10 minutes, watching carefully. Once the cookies are cool, dust the tops with powdered sugar, if desired.
*If you can’t find mint-flavored chocolate morsels, use semisweet ones and add 1 teaspoon of mint extract when you add the eggs to the batter.