Preheat oven to 350°F. Line baking sheets with parchment paper.
In a large bowl with an electric mixer, combine pumpkin, sugar, vegetable oil, egg, and vanilla. In small bowl, combine the baking soda and milk and add to pumpkin mixture. In a separate bowl, stir together flour, baking powder, pumpkin pie spice, and salt. Stir in white chocolate chips.
Using a medium cookie scoop, (about 1 1/2 tablespoons) drop cookie dough 2 inches apart onto prepared cookie sheets. Bake 8-10 minutes or until lightly browned and firm. Allow cookies to rest on the baking sheets for about 3 minutes before moving to a wire rack to cool completely.
Cookies will store in an airtight container at room temperature for up to 3 days.