Combine confectioners' sugar and almond flour in a food processor. Pulse until blended and finely ground. Line 2 large baking sheets with parchment paper. Heat oven to 350°.
Whip egg whites and salt in a stand mixer on medium-high speed until frothy. Gradually beat in granulated sugar, 1 tbsp at a time, until stiff peaks form, about 2 minutes.
Fold one-third of the confectioners' sugar mixture into beaten whites. Fold in remaining confectioners' sugar mixture and the food coloring. Transfer to a large piping bag (use half the batter so bag is not overfilled) and snip off a 1/2-inch opening.
Pipe batter in 1 1/4-inch circles onto parchment paper. Let stand at room temperature for 15 to 20 minutes.
Bake cookies, 1 sheet at a time, at 350° for 15 minutes. Cool completely on paper on wire racks.
Place chopped chocolate in a small bowl. In a small saucepan, heat cream just until steaming. Pour over chocolate and stir until smooth. Refrigerate until good spreading consistency.
Beat butter until smooth. Add confectioners' sugar and salt; beat on low speed until blended. Add heavy cream and beat until good spreading consistency. Divide in half; tint half orange with gel food coloring.
Carefully remove cookies from parchment. Spread ganache or white or orange filling onto flat side of a cookie. Sandwich with a second cookie. Repeat with all cookies.
