In a small saucepan over medium heat melt and brown your butter. A good trick is once the butter stops making popping sounds, it is done and should be immediately taken off the heat.
In a large mixing bowl, combine the hot butter, brown sugar, and granulated sugar. Mix until combined.
Add the vanilla and eggs, stir until combined.
Add the flour, salt & cream of tartar. Mix until the dough forms.
Pour the white chocolate chips into the mixture and fold in
Spread the batter out onto a sprayed and parchment paper lined 9x13 pan
Bake for 30 minutes.
Remove and allow to cool for 10 minutes before slicing.