1. Line an 8×8 pan with parchment paper. On the stovetop in a medium sized saucepan, melt the butter on low until it’s just melted. Add the brown sugar and let the mixture simmer for a couple of minutes, before adding the vanilla extract and stirring to combine.
2. Add the rolled oats and stir to coat, cooking over low for 3-4 minutes, stirring constantly. Remove the mixture from heat, then empty half of the mixture in to the parchment lined baking pan. It doesn’t need to be exactly half, just use your best guess! You can use the bottom of a measuring cup coated with nonstick spray to press the mixture as hard as you can into the bottom of the pan, in an even layer. Place the pan in the fridge while you prepare the rest of the ingredients.
3. In another saucepan, over low heat on the stove, combine together the sweetened condensed milk together with the chocolate chips. Stir constantly, until the mixture is smooth and melted together. Remove the saucepan from heat.
4. Remove the baking pan from the fridge and spread the chocolate mixture over the top of the oats, using a spatula to smooth it around in an even layer. Add the remaining oatmeal mixture in spoonfuls to the top of the chocolate layer, spreading out the spoonfuls a bit to flatten them. Leave some chocolate to peek through the oats.
5. Place the entire pan in the fridge for up to 2 hours to set completely before slicing into 16 even bars. 

Store the bars in the fridge in an airtight container, or at room temperature for 2-3 days. The bars will be softer at room temperature and may crumble a bit more. 

Bars can also be stored in the freezer in an airtight container for up to 2 months.