Grease a 9 x 13-inch baking pan and preheat the oven to 350 F.

In a medium bowl, whisk the sweetened condensed milk with the peanut butter and vanilla until smooth and well blended. Set aside.

In a separate bowl, combine the oats, flour, brown sugar, salt, and baking soda. Mix to blend.

In a mixing bowl with an electric mixer, beat the butter until it is smooth and creamy. Add the oat mixture and mix until crumbs are formed.

Pat about 2/3 of the oat mixture in the prepared baking pan. It will be sticky, so you might need to wet your hands a few times.

Drizzle with the peanut butter and sweetened condensed milk mixture. The mixture will be thick, but will slowly drizzle. Try to avoid spreading with the spoon at this point as it will lift the oat mixture. When all of the peanut butter mixture is drizzled evenly over the oat crust, wet a spatula and gently spread it over the crust.

Sprinkle the chocolate chips evenly over the peanut butter and sweetened condensed milk layer.

Sprinkle the remaining oat mixture over the chocolate chips.

Bake the peanut butter bars until lightly browned, about 20 minutes.

Remove the bars from the oven and place the pan on a rack. Cool for at least 1 hour before slicing into bars.