Preheat the oven to 350°F. Line a 9x13 baking dish with parchment paper, spray with non-stick cooking spray and set aside.
Mix together melted butter, eggs, egg yolk, and strawberry cake mix in a medium mixing bowl. Use a hand mixer or stir by hand.
Spread batter into prepared baking dish. Bake for 18 minutes.
While the brownies are baking, prepare the glaze by whisking together powdered sugar, strawberry extract, and enough water to form a paste.
Remove the brownies from the oven and immediately pour glaze on top. Spread carefully to cover the top of the brownies. (You can lift the brownies from the pan by the parchment paper if you wish before spreading the glaze on.)
Allow brownies to cool completely and the glaze will set so that it’s dry to the touch. Cut into pieces and serve.