Preheat oven to 350°F/180°C. Butter a large rimmed baking sheet.
Sift first 4 ingredients into medium bowl. Using electric mixer, beat butter in large bowl until fluffy. Add the 1/2 cup sugar and vanilla; beat until blended. Add flour mixture and beat until moist clumps form. Mix in oats with spatula until evenly distributed (dough will be very firm). Add chocolate chips and knead gently to blend.
Using moistened palms, shape 1 generous tablespoon dough into ball. Place on prepared sheet; flatten to 2-inch round. Repeat with remaining dough, spacing rounds about 2 inches apart. If desired, sprinkle tops with granulated or coarse white sugar.
Bake cookies until center is slightly firm and top is cracked, about 14 minutes. Cool on sheet.
Makes 12 cookies.
Date: May 15, 2006