Gather the ingredients - * Butter * Dark brown sugar * Granulated sugar * Eggs * Vanilla extract * Flour * Baking powder * White chocolate chips
In a large bowl, whisk together the melted butter, brown sugar, and granulated sugar.
Whisk in the eggs and vanilla extract.
Add the flour and baking powder, folding in the dry ingredients until no large lumps remain.
Fold in the white chocolate chips, if using.
Pour into the prepared baking dish and bake until an inserted toothpick comes out clean - about 28-30 minutes.
Cool completely in the pan and then slice and enjoy.
Store leftovers in an airtight container at room temperature for up to 5 days.