If you're using butter, melt it in a microwave-safe bowl. If you're using margarine, you don't need to melt it.
Add the butter, sugars and vanilla to a mixing bowl. Stir to combine.
Add the eggs and stir until combined.
Add the salt, baking powder and baking soda.
Add the flour a little at a time, mixing until it is fully combined.
Place the macadamia nuts in a zip-top bag and crush them with a rolling pin. You can leave them whole, but breaking each nut into 3–4 pieces makes the cookies easier to eat.
Mix in the macadamia nuts and white chocolate chips.
Line two baking sheets with parchment paper, foil or silicone baking mats. No greasing is needed.
Scoop the dough into 24 equal-sized balls and divide them between the prepared baking sheets.
Chill the portioned dough for 1 hour, if desired, to help reduce spreading. If you skip chilling, bake 8 cookies per sheet instead of 12 so they do not run together.
Bake at 350°F for 11–13 minutes, until the edges are just beginning to brown. Let the cookies firm up on the baking sheets before serving.