Preheat oven to 350 degrees F. Line 12 muffin cups with bake cups or lightly coat with nonstick cooking spray; set aside. In food processor finely grind nuts with 2 tablespoons sugar, 1/4 teaspoon salt, and cinnamon. Add 1 tablespoon orange juice; process until combined. Using a rounded teaspoon, shape some nut mixture into 12 balls; set aside remaining.
Combine flour, baking powder, and 1/4 teaspoons salt; set aside. beat butter with mixer 30 seconds; beat in 2/3 cup sugar. Beat in egg, orange juice, and milk on low until combined. Gradually add flour mixture; beat just until combined. Spoon half of batter into cups; top with walnut balls, pressing in lightly. Top with remaining batter. Bake about 20 minutes or until tops spring back when lightly touched. Cool in pans 5 minutes. Remover and cool on rack. Spread frosting; top with reserved nut mixture. Makes 12 muffins.
In bowl beat butter, whipping cream, and orange peel with mixer on low speed until just combined. Add powdered sugar. Beat on medium speed until smooth. Makes about 1 cup.