In medium bowl, mix first 4 ingredients until well combined; set aside.
In large bowl with electric mixer on medium speed, cream butter and 1 cup of the granulated sugar until light and fluffy. Beat in sour cream, eggs and vanilla.
Beat in half the flour mixture until just combined. Stir in remaining flour mixture with a spoon (dough will be very soft). Spoon dough by heaping tablespoons on prepared baking sheets about 3 inches apart, making about 24 cookies.
Butter the base of a flat bottomed glass that about 3 inches wide. Dip bottom of glass into the remaining 1/4 cup granulated sugar. Use sugared glass to flatten cookies into 3 inch rounds, coating bottom of glass with sugar each time.
Sprinkle cookies with some coarse sugar.
Bake for 10 to 12 minutes, or until tops spring back when lightly pressed. (Cookies will be very light in color).