Prepare the crust as directed, pressing it into a 9 1/2" to 10" deep-dish pie pan. Prebake as directed and cool on a rack. Set the oven to 325°.
Combine the cream cheese and peanut butter in a large mixing bowl. (If you have one, a stand mixer works well here.) Using an electric mixer, cream the ingredients on medium speed. Gradually add the sugar, beating until evenly blended and scraping down the sides of the bowl as needed. Blend in the eggs and yolk, one at a time, until evenly blended. Blend in the sour cream and vanilla. Blend in the chopped nuts.
Scrape the filling into the pie shell and smooth the top with a spoon. Place on the center oven rack and bake for approximately 50 minutes. When done, the filling will have puffed slightly and the center will be wobbly, but "set." The very center may have a shiny finish but the rest of the surface will have a dull appearance.
Transfer the pie to a rack and cool thoroughly. Cover loosely and refrigerate at least 8 hours or overnight.
The next morning, finish the pie with the chocolate topping and garnish. Heat the cream in a small saucepan until the surface shimmers. Remove from the heat and add the chocolate. Let sit for 7 or 8 minutes, then whisk to smooth.
As the chocolate cools, it will start to thicken. When it is still thin enough to drizzle but has a fair amount of body, drizzle half of the chocolate over the surface of the pie with a large spoon. Distribute the chopped peanut butter cups here and there over the chocolate, then drizzle the rest of the chocolate over the top. Refrigerate until serving. Cover with tented foil for extended refrigeration. Makes 10 to 12 servings.