Place a standard loaf pan in the freezer to chill.
Melt the peanut butter chips and chocolate chips (separately) in the microwave according to the instructions on the bags. Set aside to cool slightly.
In a large bowl, mix together the condensed milk, vanilla and 1 cup of mini Reese's until combined.
In a separate bowl, whip the cream until stiff peaks form. (It will literally look like whipped cream.) As soon as you have stiff peaks, whip in the peanut butter until just combined.
Fold the cream mixture gently into the condensed milk mixture with a spatula. Pour half of it into the chilled pan. Spoon dollops of melted chocolate and melted peanut butter on top (about half). Use a knife to cut the chocolate and peanut butter into the ice cream, forming a swirl pattern. Note that the swirl won't be very pronounced, but you'll end up with little chunks of peanut butter and chocolate throughout. Pour the remaining ice cream on top, and repeat the dollops and swirl with the remaining chocolate.
Top with more mini Reese's. Place in the freezer to chill for at least 4 hours before serving. Cover the pan with foil after the ice cream has chilled for about an hour. Enjoy!