Preheat the oven to 375 degrees F. Line a cookie sheet with parchment paper.
Combine the flour, baking soda, baking powder, and salt in a mixing bowl.
Using a mixer, beat the butter in a large mixing bowl until fluffy, about 2 minutes. Add the brown sugar and mix together until smooth.
Add the egg and vanilla. Stop to scrape down the sides of the bowl with a rubber spatula. Blend in the flour mixture in 3 stages and stir in the white chocolate and the nuts.
Scoop out walnut-sized mounds of the cookie dough and place on the cookie sheet, leaving 2-inches between the mounds. Bake for 8 to 10 minutes, until the cookies are golden. Remove the cookie sheet from the oven and transfer the cookies from the parchment to cooling racks. Store in an airtight container at room temperature for up to a week. Freeze for longer storage.