Pistachio Whipped Shortbread Cookies With Chocolate

Preheat oven to 350°F. Line 2 baking sheets with parchment paper or a silpat.
In a small food processor, blend the cane sugar until fine and powdery, like icing sugar.
Transfer the sugar to a large bowl. Add the butter and vanilla extract. Beat until the mixture is light and fluffy with a very pale yellow color, stopping to scrape the sides as necessary. This takes about 3 minutes.
Add the pistachio flour and cornstarch to the butter mixture. Beat for another 3 minutes. The dough should look like frosting.
Transfer the cookie dough to a parchment piping bag. Pipe into mounds that are 1 1/2 inches tall on the 2 prepared baking sheets.
Bake until the edges are just lightly golden, about 11-12 minutes. Don't let them darken too much! If both sheets won't fit in your oven at the same time, it's okay to keep one out at room temperature.
Let cookies cool on the pan for 10 minutes. Then gently transfer them to a wire rack to finish cooling. They'll be very delicate.
Once cookies have completely cooled, drizzle with melted chocolate and sprinkle with sea salt.