Macaron Shells: Beat the egg whites until foamy, then add the granulated sugar and food coloring. Whip until stiff peaks form and the meringue is glossy and holds a bird’s beak shape. In a large bowl, sift together the almond flour and powdered sugar. Add one-third of the meringue to the dry ingredients to loosen the mixture, then fold in the remaining meringue. Gently mix until the batter flows in ribbons.

Using a piping bag fitted with a plain round tip, pipe the macarons onto a baking sheet lined with parchment paper. Let them sit at room temperature for 30 minutes to form a skin. Bake at 275°F (135°C) for 17 minutes.

Ganache: In a saucepan, bring the passion fruit puree to a boil. Place the chopped milk chocolate in a large bowl. Pour the hot puree over the chocolate in three additions, mixing well each time to emulsify. Add the butter in small pieces and mix until smooth. Let the ganache set in the refrigerator or at room temperature for several hours.