Pour 2 cups of COLD heavy whipping cream into the bowl of a Kitchen Aid stand mixer or into a regular large bowl if using a hand mixer. Using the whisk attachment of a Kitchen Aid stand mixer mix for 3-4 minutes on medium-high or until the whipping cream has formed stiff peaks. Alternately, do the same thing using a hand mixer.
Pour 1 14 oz. can of sweetened condensed milk into a separate large bowl.
Add 1 scoop of the whipped cream to the condensed milk and slowly stir to combine. Continue to add the whipped cream, 1 scoop at a time, folding each scoop in using a spatula. Continue until all the whipped cream is added. Be careful not to over-mix or the mixture will deflate and become watery.
Refrigerate 8 Reese's Peanut Butter Cups (this will prevent them from melting as you handle them). Remove from the fridge and chop them into bite-size pieces. Fold the pieces of candy into the ice cream mixture being careful not to over-mix.
Pour the ice cream mixture into a metal bread pan or loaf pan. Drizzle ⅓ cup or so of chocolate syrup into the ice cream and swirl it together using a spatula.
Smooth the top of the ice cream out with a spatula. Place a piece of wax paper or plastic wrap over the top of the bread pan. Press down on the wax paper, smoothing it out across the surface of the ice cream (this will prevent ice crystals from forming).
Place the bread pan in the freezer and allow to harden for at least 6 hours or overnight if possible.
To serve: Remove from freezer a few minutes before serving so that it's easier to scoop. Top with more chopped Reese's Peanut Butter Cups and a sprinkle of salt.
Notes
This ice cream lasts up to 2 weeks wrapped tightly in the freezer.