1 pound butter, room temperature
1 cup icing sugar
1/2 cup cornstarch
3 cups all-purpose flour
1 tsp pure vanilla extract
In the bowl of an electric mixer fitted with the paddle attachment, cream butter until smooth. Sift together icing sugar, cornstarch and flour. Gradually add to creamed butter, in fourths or fifths, beating slowly until just combined. Add vanilla, then increase speed to high and whip for about 10-15 minutes, occasionally stopping to scrape down sides with a rubber spatula. Batter is finished when it is very fluffy and white.
Add batter to a large pastry bag fitted with a star tip. Pipe onto Silpat-lined baking sheets and bake at 350F for about 15 minutes. Do not allow to colour. Let cool completely on sheets.
To store in batches for Christmas, transfer cookies to airtight containers, lining each layer with paper towel or parchment paper. Freeze for up to a month.