Line a 8x8 or 9x9 pan with foil or parchment paper (optional). Spray pan or liner with cooking spray.
Mix the lemon cake mix, oil, eggs, vanilla and lemon juice together in a large mixing bowl. Batter will be thick.
Spread evenly in pan.
Bake for 20 minutes or until center is set.
Let cool.
Frosting
In a small saucepan, melt the butter over medium low heat.
After the butter is melted, stirring frequently, let the butter simmer until the butter turns a darker color.
Remove from heat and whisk in powdered sugar.
Stir in the lemon juice.
Frost the lemon brownies.
Serve
Notes
You may need to add additional powdered sugar to the melted butter. It depends on the thickness of the frosting. For a glaze, you will need less powdered sugar. For a spreadable frosting, you will need more powdered sugar. Add a little at a time to get the desired amount you want.