Preheat the oven to 300 degrees F. Cream the butter with the sugar using a handheld mixer. Mix in the rosemary, salt, and flour, 1/4 cup at a time. Sprinkle in the chocolate chips, and stir by hand until well-distributed. Gather the dough into a ball. (If the dough begins to soften or feel greasy, chill the dough for 15 minutes.)
Roll the dough out into a rectangle of 1/2-inch thickness and cut into rectangles about 1/2-inch by 2-inches. Place the dough pieces on a cold ungreased baking sheet. Prick the tops with a fork. Bake the shortbread until the dough starts to turn a golden color, about 25 minutes. Remove the shortbread from the baking sheet and let cool completely on a rack.