These Brown Sugar Fingers are a variation of our Basic Shortbread Wedges. The secret to shortbread's tender, crumbly nature is stirring the wet and dry ingredients until they are just combined.
Butter an 8 1/2-inch cake or springform pan; set aside. Sift together flour and salt into a small bowl; set aside. Place butter in bowl of electric mixer fitted with paddle attachment. Cream until fluffy, 3 to 5 minutes. Add sugar, and continue to beat until very light in color and fluffy, occasionally scraping down the sides of the bowl with a spatula, about 2 minutes more. Add vanilla, if using. Add flour mixture, and combine on low speed, scraping with spatula if necessary, until flour is just incorporated and dough sticks together when squeezed with fingers.
Pat dough into prepared pan. If rolling out dough to cut into shapes, form into a flat disk; wrap in plastic. Chill until firm, at least 1 hour.
Roll into a rectangle about 1/2 inch thick, and about 5 by 12 inches long. Trim the ends to make a perfect rectangle. Score the dough crosswise into 3/4-inch-wide strips, and, using a fork, make a decorative pattern on each strip if you like.
Heat oven to 325 degrees. Bake until firm, about 30 minutes. Cut into fingers once they have cooled.