Preheat oven to 350° F. Line a 9x9 baking pan with parchment paper, spray with nonstick spray and set aside.
In a medium bowl, whisk together the flour, baking soda and salt. Set aside.
In the bowl of a stand mixer fitted with a paddle attachment, beat on medium speed the butter, brown sugar and granulated sugar until light and fluffy, about four minutes. Scrape down the sides of the bowl when necessary. Add the egg and vanilla. Beat until combined, 20 to 30 seconds.
With the mixer on low, slowly add the flour mixture to the dough. Careful not to over beat. With a wooden spoon or rubber spatula, stir in the chocolate chips by hand.
Scoop cookie dough into prepared baking dish. Press and disperse until the bottom of the pan is covered. Bake for about 15 minutes or until the edges start to turn golden and the center is set. Remove and cool slightly.
Fudge Layer
In a microwave safe bowl, stir together sweetened condensed milk with chocolate morsels. Heat in 20 second intervals on medium power level, stir, and heat an additional 20 seconds. Continue until smooth and creamy. (It's okay if a few of the chocolate chips aren't melted all the way).
Spread evenly over baked cookie bars. Immediately sprinkle with chopped Snickers bars.
Refrigerate for 2 hours (or overnight) until the fudge layer is set. Cut into squares and store in an airtight container for up to a week.
Notes
*Alternatively, you can use store bought cookie dough for this layer. I suggest using about 16 ounces (about two cups). **Or 12 fun-sized Snickers bars, chopped.