Preheat the oven to 350°F. Grease a 9x13 inch baking dish with cooking spray, set aside. With a hand mixer and a large bowl or in the body of a stand mixer with the paddle attachment, mix the butter, brown sugar, and egg yolk together until fluffy, about 3 minutes on medium speed. Add in the flour, vanilla, and salt, mix until just combined, scrape down the sides as needed.
Press the dough into the greased baking dish. To make this easier, lightly wet your fingertips and press the dough into an even layer. Bake for 20-25 minutes, the crust will puff up and it is ready when it is golden brown along the edges. Let sit 5 minutes so the crust can deflate. Add the chocolate chips on top and wait until they are melted, you know they are ready when the chocolate turns glossy, about 5 minutes.
Smooth out the chocolate with a spatula to coat the crust, I like to leave a border of crust for presentation, but that is optional. Sprinkle the toffee bits on top evenly. Let cool completely and cut into portions.