Preheat oven to 180 degrees. Line a 12 muffin pan.
Whisk together all the wet ingredients, from pumpkin puree to yogurt till smooth.
In a large bowl, whisk together all the remaining ingredients including the chocolate chips. Add the wet ingredients and fold in till moist.
Divide equally into the muffin cups. Bake for 30 minutes or till a skewer comes out clean.
Cool completely on a wire rack.
For the frosting, whip the butter till smooth. Add the icing sugar, 1/2 cup at a time till combined. Reserve 1/2 cup for the whipping cream.
In another bowl, whip the cream till smooth. Add the reserved icing sugar and whip till done. Add in the vanilla and whip till stiff.
Fold in the whipped cream into the buttercream lightly till combined. Fold in the peanut butter. Refrigerate till use.
Once the muffins are completely cooled, top with the cold frosting. Serve.