For the Cookie: 

Adjust oven rack to the middle position and preheat to 350°F. 

In a food processor, combine the pistachios, white chocolate chips, white sugar, flour, roses, salt and baking soda. Pulse the dry ingredients until it resembles chunky sand. 

Transfer the dry mixture into a large bowl and add in the melted butter and egg yolk. Using a rubber spatula, stir the mixture until a ball is formed. 

Roll the dough into 1-tablespoon sized portions on a parchment-lined sheet pan and flatten the cookie dough into disks. Be sure to leave at least 2 inches between each cookie.

Bake until lightly brown, about 10 minutes. Allow cookies to cool on the baking tray. 

For the Décor: 

Melt the chocolate and drizzle over cooled cookies. Sprinkle crushed rose petals over the top for a finishing touch.