Preheat the oven to 350 degrees Fahrenheit.
Beat the butter, sugars, and tahini together until light and creamy. Add the egg and beat again.
Sift the flour, salt, and baking powder twice. Use a spoon to fold into the tahini mixture. Add walnuts and mix by hand. Add a tiny splash of almond milk if the dough is too dry/crumbly to form into balls.
Roll dough into balls and place on greased baking sheet. Lightly press with the tines of a fork to make a criss-cross pattern on the top of the cookies.
Bake for about 20 minutes (mine baked for 23) until lightly colored. Cool on tray for 5 minutes, then transfer to wire rack to finish cooling. Store in an airtight container.