Preheat oven to 350 degrees. Arrange pecans in a single layer on a rimmed baking sheet; toast in oven until fragrant, about 10 minutes. Remove from oven (leave oven on); set aside 36 pecans on baking sheet. Finely chop remaining pecans (for about 1/4 cup); set aside.
When pecans are cool enough to handle, make 12 clusters by arranging 2 pecans vertically, side by side, below 1 pecan placed horizontally. Gently flatten each caramel; place 1 on top of each cluster. Bake clusters 5 minutes. Remove from oven (leave oven on).
Place 1 piece of chocolate on top of each cluster. Return to oven; bake until chocolate begins to melt, 1 to 2 minutes. Remove from oven.With the back of a spoon, gently spread chocolate over caramel without completely covering it.
Sprinkle clusters with reserved chopped pecans. Refrigerate until set, about 15 minutes. Bring to room temperature before serving.