Preheat fryer to 375 degrees F. with canola oil.
In a medium sized bowl, cream together shortening, mascarpone and sugar. In a measuring cup mix together buttermilk, egg, vanilla, lemon juice and zest. Slowly beat in egg mixture. Once well blended slowly add flour, baking soda, baking powder and salt.
Roll dough out on a floured surface until 1/3-inch thick. Punch out doughnuts with a 1 1/2-inch biscuit cutter or donut cutter. Let stand 10 minutes. Fry until golden. Remove from fryer and dust with powdered sugar. Serve with fresh berries.