Heat oven to 375°F. Whisk together flour, baking soda, and salt. In a large bowl, with an electric mixer on medium, beat butter, shortening, and peanut butter until fluffy. Add sugar and beat until combined. Beat in egg and vanilla.
Pull off tablespoonfuls of dough and form into balls. Dip one side into crystal sugar and place sugar-side-up on baking sheets 1-1/2 inches apart; flatten slightly.
Bake 10 to 12 minutes, until edges are a light golden brown. Press 4 nonpareils in a buttonhole pattern in the center of each cookie and bake another 2 minutes. Cool on baking sheets 5 minutes. Transfer to wire racks and cool completely. Repeat with remaining dough.