Preheat oven to 180 degrees Line a 12-cup muffin tin with muffin cases. Line a second muffin tin with 4 cases or alternatively line a mini muffin tin with 10 cases.
In a bowl combine cornstarch, flour, baking powder, baking soda and salt and set aside.
In a large bowl beat together butter, oil and sugar until homogeneous. Add eggs, one at a time. Add in vanilla, cider and yogurt and mix until smooth. Gradually add the dry ingredients and mix at a lower speed, just until incorporated in the batter.
Spoon the batter into the muffin cases filling them 2/3 full. Bake for about 20-25 minutes or until a toothpick inserted in the center comes out clean. Remove the pan from the oven, let the cupcakes cool for 2-3 minutes and then transfer them to a wire rack. Frost them after they cool down to room temperature.
In a large mixing bowl beat together cream cheese, powder sugar, sour cream and pear jam. Add the chocolate, melted over a pan of simmering water, and beat quickly before it hardens (to avoid issues, before starting the frosting make sure that the sour cream and the cream cheese are at room temperature and not cold). When the frosting is homogeneous, place the bowl in the freezer for 10 minutes to thicken.
Use a piping bag or an icing knife to frost the cupcakes. Decorate with fresh or candied pears.