Start by browning your butter—this is where a lot of the flavor comes from.
Place the butter in a saucepan over medium heat and let it melt. Keep stirring as it cooks. After a few minutes, it will start to foam, then turn a warm golden color with little brown specks at the bottom. It should smell rich and slightly nutty.
As soon as you see those brown bits, remove it from the heat. Let it cool for about 10–15 minutes so it doesn’t scramble your eggs later.
In a large bowl, whisk together the browned butter and both sugars until well mixed.
Add the peanut butter, egg and extra egg yolk, milk then pour in the vanilla. Stir until everything is fully combined and creamy.
In a separate bowl mix together flour, oats, salt, baking powder, baking soda, and cinnamon.
Combine dry into wet and gently mix just until everything comes together.
Fold in the chocolate chips and M&M’s until evenly distributed.
Cover the bowl and place it in the fridge for at least 30 minutes (up to an hour is even better).
This step makes a big difference. It helps the cookies bake up thicker, chewier, and more flavorful.
Preheat your oven to 350°F and line a baking sheet with parchment paper.
Scoop the dough into large balls (about 2–3 tablespoons each) and place them a few inches apart on the baking sheet.
Bake for 10–12 minutes, just until the edges are set and the centers still look slightly soft.
Let the cookies cool on the pan for a few minutes before transferring them to a wire rack. These cookies will continue to set as they cool, so don’t overbake them.
