Preheat the oven to 350°F. Spray a 12-14 cup bundt pan with baking spray or butter and flour. Set aside. (You can also bake this in an angel food pan)
To make Cake: Using an electric mixer, cream together the butter, peanut butter and vanilla in a large bowl for 1-2 minute. Beat until completely smooth.
Add granulated sugar and brown sugar. Beat until fluffy and combined on medium-high for 2-3 minutes.
Add the eggs one at a time beating well after each addition.
In a separate medium bowl, use a whisk to sift together the flour, baking powder and salt. Lower the speed of the mixer to medium-low add the sifted dry ingredients alternately with the buttermilk beginning and ending with flour.
After all has been added, scrape the sides of the bowl then beat for around 1 minute or just until fully combined.
By hand, mix-in the chopped Reese's cups, milk chocolate and peanut butter chips. (Reserve 1/2 cup of chopped Reese's for garnishing)
Spread evenly into the bundt pan. Bounce on the counter to settle the batter.
Place into the oven and bake for 1 hr 15 to 1 hr 30 minutes OR until a tester inserted into the center comes back clean. Check halfway through baking and lay a piece of aluminum foil on top to prevent over browning, if needed.
Cool in the pan for 20 minutes then carefully turn onto a cooling rack to cool completely.
To make Glaze: In a medium-size microwave safe bowl melt together the chocolate chips, heavy cream and peanut butter. Heat in 20-30 second increments stopping to stir each time. Add additional cream as needed, until pourable.
Drizzle over the cooled cake then sprinkle with reserved chopped Reese's cups.
Store tightly sealed chilled or at room temperature.