Line a 9-inch x 9-inch baking dish with parchment paper or foil. spray with a light coat of non-stick cooking spray. Set aside.
Place the NESTLÉ® TOLL HOUSE® Dark Chocolate Morsels in a glass bowl.
Pour the sweetened condensed milk into a microwave-safe bowl and heat it in the microwave for 1 minute. Pour the sweetened condensed milk over the chocolate and allow it to sit for 30 seconds.
Use a rubber spatula to mix the hot milk and chocolate together until the chocolate is smooth. (Sometimes I have to microwave the chocolate mixture for 20 seconds at a time to help everything melt properly.)
Place 1/2 of the chocolate mixture into your prepared baking dish. Use the back of a large spoon to spread the chocolate evenly in the pan and smooth out the top of the layer.
In a medium sauce pot, heat the brown sugar, heavy cream & butter over medium-high heat until the butter melts and the sugar is dissolved.
Place a candy thermometer in the pot and bring the caramel mixture to a boil. Whisk occasionally, and cook until the caramel reaches 245 degrees F (soft ball temperature). Remove the caramel from the heat and whisk in the vanilla.
Pour the caramel over the fudge layer in your baking dish. Carefully tilt the dish so that the caramel spreads into each corner and to the sides.
Sprinkle half of the toffee bits over the caramel.
Carefully spread the rest of the fudge mixture over the caramel layer. (I plop big dollops around the dish and then use the back of the spoon to spread the chocolate out.)
Sprinkle the top of the chocolate with the remaining toffee bits. Use your hand to lightly press the toffee into the chocolate.
Let the fudge set up at room temperature for 2 hours. If the fudge it's set up enough to your liking, you can transfer it to the refrigerator for 30 minutes to an hour.
Use the parchment or foil to remove the fudge from the baking dish. Carefully pull the paper or foil off of the fudge. Use a sharp knife to cut the fudge into 32 pieces.
You can use the plain toffee bits or the ones that have chocolate on them too. Either is fine.If not serving this fudge immediately, store in an airtight container in the fridge.