Line a 9x13 inch baking pan with parchment paper, leaving an overhang on the sides for easy removal. Lightly spray the parchment paper with non-stick cooking spray.

Place 1 cup of all-purpose flour in a microwave-safe bowl. Microwave on high for 60-90 seconds, stirring every 30 seconds, until the flour reaches an internal temperature of 160°F (71°C). This step is crucial for food safety. Let the flour cool completely before using.

In a large mixing bowl, using an electric mixer or by hand, cream together the softened unsalted butter, packed light brown sugar, and granulated sugar until light and fluffy (about 2-3 minutes).

Beat in the milk and vanilla extract until well combined.

Gradually add the cooled, heat-treated flour and salt to the wet ingredients, mixing on low speed until just combined and no dry streaks remain.

Stir in the creamy peanut butter and old-fashioned rolled oats. Finally, fold in the 1/4 cup mini chocolate chips and 1/4 cup mini M&M's. Set the edible cookie dough aside.

In a large, heavy-bottomed saucepan, melt 1/2 cup (1 stick) unsalted butter over medium heat.

Add the evaporated milk and 3 cups of granulated sugar to the saucepan. Bring the mixture to a full rolling boil, stirring constantly to prevent scorching.

Continue to boil for exactly 5 minutes, stirring frequently.

Remove the saucepan from the heat. Immediately stir in the entire jar of marshmallow fluff until it is completely melted and the mixture is smooth.

Add the 2 cups of white chocolate chips and 1 tsp vanilla extract. Stir vigorously until the white chocolate is fully melted and the fudge is smooth and glossy.

Pour about half of the hot fudge mixture into the prepared 9x13 inch pan and spread it evenly with a spatula.

Drop spoonfuls of the edible monster cookie dough over the fudge layer, distributing them as evenly as possible.

Carefully pour the remaining hot fudge over the cookie dough and gently spread to cover.

Immediately sprinkle the remaining 1/4 cup mini chocolate chips, 1/4 cup peanut butter chips, and 1/4 cup mini M&M's over the top of the fudge, gently pressing them into the warm fudge.

Let the fudge cool at room temperature for about 30 minutes, then transfer it to the refrigerator. Chill for at least 2-3 hours, or until the fudge is completely firm.

Once firm, use the parchment paper overhang to lift the fudge out of the pan. Place it on a cutting board and use a sharp knife to cut it into 1 to 1.5-inch squares. For cleaner cuts, wipe the knife clean with a damp cloth after each slice.