Place butter in a medium-sized saucepan allow it to melt, and then brown- getting golden around the edges and then a nice rich brown color. Allow to cool slightly.
In a bowl stir together the flour, baking soda, salt and cream of tartar.
Pour the butter into a large bowl with the brown sugar and stir until smooth. Add the vanilla extract, egg, and egg yolk and mix until smooth.
Add the dry ingredients and mix slowly until well incorporated but don't over-mix.
For large, thick cookies- divide dough into about 9 portions, rolled into balls and flattened slightly. I just eye balled it, but I'd say about ⅓ cup of dough went into each one. You can of course portion them smaller for more average sized cookies.
Freeze dough rounds for 5-10 minutes before baking, then bake at 350 for 13-15 minutes or until the edges feel done and the tops have cracked a bit. (Bake less for smaller cookies.)
Notes
*Regular brown sugar would work too but I like the richer flavor from the dark.
*Cream of tarter helps add the crackled texture to the tops of the cookies, but is optional.
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