Line an 8 1/2-by-4 1/2-inch loaf pan with a piece of wax paper or parchment, allowing the paper to hang over both long sides.
In a large bowl, beat the cream and sugar until stiff peaks form.
In the bottom of the pan, arrange 3 of the sandwiches in a single layer, cutting them to fit as necessary. Spread with half the whipped cream. Repeat with the remaining sandwiches and whipped cream.
Sprinkle the top of the cake with the chopped candy bar. Cover with plastic wrap and freeze until firm, at least 1 hour and up to 1 week.
Holding both sides of the paper overhang, lift the cake out of the pan and transfer to a platter. Discard the paper, slice the cake, and serve.