Salted Butter and Chocolate Chunk Shortbread

1 cup plus 2 tbsp (2¼ sticks) cold salted butter, cut into ½ inch pieces
½ cup sugar
¼ cup (packed) light brown sugar
1 tsp vanilla
2¼ cups flour
6 ounces semi-sweet chocolate or bittersweet dark chocolate, chopped into chunks
1 egg, beaten to blend
Demerara sugar (for rolling)
sea salt

Using an electric mixer and a medium bowl or a stand up mixer fitted with the paddle attachment, beat butter, sugars and vanilla and  medium-high speed until light and fluffy, about 3-5 minutes.

Scrape down the sides of the bowl. With mixer on low speed, slowly add flour, followed by chocolate chunks, and beat just to blend.

Divide dough in half. Form each half into a log shape about 2-2¼ inches in diameter. Rolling it on the counter will help smooth it out. Chill until firm, about 2 hours.

Preheat oven to 350 degrees. Line baking sheets with parchment paper. Brush outside of logs with egg wash. Roll logs in demerara sugar.

Slice each log into ½” thick rounds.  Arrange on prepared baking sheet about 1” apart. Sprinkle with sea salt. Bake until edges are just beginning to brown, about 12-15 minutes.

NOTE: Cookie dough can be made 1 week ahead. Tightly wrap in plastic and chill, or freeze up to 1 month. Cookies can be baked 5 days ahead. Store in plastic wrap or an airtight container.