Preheat oven to 350F and line an 8×8-inch baking pan with aluminum foil, spray with cooking spray; set aside.
To a large saucepan, add the milk, oats (not quick-cook or instant because they behave more like flour and recipe will not work properly), egg, brown sugar, peanut butter, cinnamon, and cook uncovered over medium-high heat, whisking frequently, for about 15 minutes, or until mixture has thickened considerably. If you’re in doubt if it’s thick enough, it’s better to err on the too-thick-side than not-thick-enough. Once mixture starts to boil, allow it to really bubble, making sure to whisk it so it doesn’t form a skin.
After about 15 minutes, remove saucepan from the heat, and add the raisins (or another dried fruit, or omit), vanilla, and whisk to combine. Use caution when adding the vanilla because it could cause the mixture to bubble up a bit.
Turn mixture out into prepared pan, smoothing the top lightly with a spatula.
Evenly sprinkle with the chocolate chips, lightly tapping them down with a spatula if necessary.
Bake for about 25 minutes, or until center is set. Baking times could range greatly based on how thick your mixture was on the stovetop, what kind of milk you’re using, oven and climate variances, etc. Bake until your bars are done to your liking, noting that they are very soft bars, shouldn’t be over-baked, and the top will be shiny even when set and done.
Source:
averiecooks.com