Heat oven to 350°F. Grease bottoms only of 32 mini muffin cups with shortening or cooking spray. In large bowl, beat granulated sugar and 1/2 cup butter with electric mixer on medium speed until fluffy. Beat in peppermint extract and egg until blended. On low speed, beat in flour, baking soda and salt.
Shape dough into 1 1/2-inch balls. Press each ball in bottom and up side of muffin cup.
Bake 9 to 12 minutes until set and edges are light golden brown. Cool 1 minute; remove from muffin cups to cooling racks. Cool completely, about 15 minutes.
In small bowl, beat filling ingredients except crushed candies with electric mixture on medium speed until smooth and creamy. Stir in 1/4 cup of the candies. Spoon or pipe 1 rounded measuring teaspoon filling into center of each tart shell. Sprinkle with remaining crushed candies.