Mix flour, oats, ginger, cinnamon, baking soda, nutmeg, and salt in large bowl.
Using a stand mixer with the paddle attachment (or a large bowl with electric mixer), cream together the butter and brown sugar in large bowl with electric mixer on medium speed until light and fluffy, about 3 minutes.
Add molasses, egg, and vanilla and beat on medium speed until fully incorporated. Using a spatula, scrape down the sides to release some of the dough.
Gradually add flour mixture, one cup at a time, on low speed until well mixed.
Fold in the white chocolate chips and evenly distribute as best you can.
Press dough into a thick flat disk. Wrap in plastic wrap. Refrigerate 4 hours or overnight.
Preheat oven to 350 degrees F. Shape dough into 1-inch balls. Roll in granulated sugar. Place 2 inches apart on baking sheets lined with parchment paper.
Bake 8 to 10 minutes or until edges of cookies just begin to brown. Remove to wire racks; cool completely.