In a small bowl, use the back of a spoon to cream the butter, peanut butter, and brown sugar together until smooth.
Add milk and vanilla extract and stir to mix thoroughly.
Add flour, rolled oats, and sea salt and mix until it's even and smooth.
Fold in mini chocolate chips and mini M&Ms.
Serve immediately in two small bowls or refrigerate for 3-4 days. Allow cookie dough to come up to room temperature before enjoying from the fridge, so it's not rock hard.
Notes
This recipe is egg-free and is safe to eat raw as long as the flour has been properly heat-treated.
To heat-treat flour: Place the flour in a microwave-safe bowl and heat it on high in 30-second intervals, stirring between each interval, until the flour reaches 165°F. This usually takes about 1 to 2 minutes. OR: Spread the flour on a baking sheet and bake at 350°F (175°C) for 5-7 minutes. The internal temperature should reach at least 165°F to kill any potential bacteria. Let the flour cool completely before adding it to the cookie dough.