Add whipping cream, powdered sugar, vanilla, and salt to the bowl of stand mixer fitted with a whisk attachment. Mix on high for 2-3 minutes, until the cream has thickened and holds its shape when the whisk attachment is turned upside down. If you do not have a stand mixer, use a large mixing bowl and a handheld mixer. Set aside until ready to use.
For the No-Bake Peanut Butter Pie with Reece's:
Add cream cheese, powdered sugar, peanut butter, butter, vanilla, and salt to the bowl of stand mixer fitted with a paddle attachment, and begin mixing on low. Turn speed to medium-high and mix until smooth and creamy. If you do not have a stand mixer, use a large bowl and a handheld mixer to mix.
Add ¾ cup of chopped Reece's Peanut Butter Cups, and mix until evenly incorporated. Spread the filling across the Oreo crust and smooth over the top.
Spoon a heaping layer of whipped cream over the peanut butter filling and smooth over the top, cover with plastic wrap, and refrigerate until completely chilled through (2-3 hours), or up to overnight, before serving.
Before serving, drizzle with chocolate syrup (if using) and sprinkle with the remaining ¼ cup of chopped Reece's.