In large bowl, beat together butter, shortening and sugar until fluffy. Beat in egg, almond extract and vanilla. In separate bowl, whisk together flour, ground almonds and baking powder; add to butter mixture and stir to form stiff dough.
Roll dough by tablespoonfuls (15 mL) into balls. Place, 2 inches (5 cm) apart, on greased or parchment paper?lined rimless baking sheet; top each with whole almond, pressing into dough. Mix egg yolk with 1 tsp (5 mL) water; brush over cookies.
Bake in centre of 350°F (180°C) oven until edges are light golden, about 15 minutes. Transfer to rack; let cool completely. (Make-ahead: Layer between waxed paper in airtight container and store at room temperature for up to 5 days or freeze for up to 2 weeks.).