Preheat oven to 350°F.
In a large bowl, beat the butter, brown sugar and maple syrup until well combined — the mixture will have the consistency of wet sand. Add the egg and vanilla and beat until smooth.
Add the flour, baking soda and salt (stir them together first only if you want to) to the butter-sugar mixture and stir by hand until almost combined; add white chocolate and walnuts and stir just until blended. It may seem dry at this point - I always find it easiest to get in there with my hands toward the end.
Drop spoonfuls of dough (or roll rough walnut-sized balls) about 2” apart on a cookie sheet that has been sprayed with nonstick spray. Flatten each a little with your hand, just to give them a head start. Bake for 10-12 minutes, or until pale golden and set around the edges but still soft in the middle. Transfer to a wire rack to cool.