Preheat oven to 325 degrees F. Spray the sides of the 9.5-inch springform pan with nonstick baking spray. Wrap the sides of the pan with a 3-inch wide strip of parchment paper.
In a food processor, pulse the peanut butter cookies until crumbs form.
Add the melted 4 tablespoons butter and pulse until the crumbs are coated with butter.
Press the crumbs firmly and evenly into the bottom of a prepared pan.
Place in the fridge to chill for 15 minutes or until firm. Work on the cheesecake batter.
Cheesecake
In a large mixing bowl, add in the 20 ounces cream cheese and 1 1/2 cups creamy peanut butter. Beat with a hand mixer on medium until creamy.
Add the 3/4 cup granulated sugar and 1 cup light brown sugarBeat until completely incorporated. Scrape the sides and bottom of the bowl.
Add in the 2 teaspoons vanilla extract and then the 4 large eggs, one at a time. Beat in each egg completely before adding the next. Scrape down the bowl after adding each egg.
Add in the 1 cup full-fat sour cream and 1/2 cup heavy cream. Mix until incorporated.
Fold in the 1 cup M&M's and 3/4 cup mini chocolate chips.
Just before adding the cheesecake mixture, wrap the outside of the springform pan with two layers of heavy-duty tin foil. I double wrap it to prevent the water from leaking in. Pour the cheesecake filling into the crust.
Place the springform pan in a larger baking pan. Fill the outer pan with about an inch of water.
Place in the oven at 325 degrees F and let bake for 1 hour 35 minutes or until done. The top of the cheesecake will be brown. To make sure the cheesecake is done, give it a wiggle. If it slightly jiggles in JUST the middle like jello, then it's done. If it jiggles all over, it needs to bake longer. Let it cool in the oven for 1 to 2 hours until it reaches room temperature and then place in the fridge to chill overnight.
Ganache
In a microwave-safe bowl, add 1 1/4 cup semisweet chocolate chips and 1 cup heavy cream.
Microwave in 30-second intervals and stir afterward. Repeat until the ganache is smooth and completely melted.
Pour about 1/3 to 1/2 of the ganache on the top of the cheesecake.
Let it rest of the ganache sit at room temperature until it thickens to a spreadable consistency. You can speed up the process by placing it in the fridge. Keep an eye on it.
While the ganache is setting up, decorate the top with 1 cup M&M's, the regular sized ones. Leave about an inch of space around the edge of the cheesecake for the piped ganache.
Add the remaining ganache into a disposable piping bag fitted with a 1M tip. Pipe swirls on the top of the cheesecake.
Notes
Storage: Store covered or in an airtight container in the refrigerator for up to 5 days.