Preheat oven to 375 degrees. Blend butter, sugars, egg, and vanilla until fluffy, stopping once to scrape down sides of bowl, about 1 minute. Add flour, baking soda and salt and mix until just combined. Do not overmix. Stir in white chocolate chunks and nuts. Mound dough by one third cupfuls onto lightly greased cookie sheet. space about 5 cm apart. Bake at 375 degrees until lightly brown around edges, about 15 minutes. Cool on cookie sheet for 3 minutes, then remove to racks and cool completely. Store in air-tight container. Can be prepared ahead, store cookies up to 4 days at room temperature or freeze 3 weeks.