Sift together flour, baking powder, baking soda and salt; set aside. In another bowl, use an electric mixer to beat together eggs and sugar until thick and pale yellow. Beat in melted butter, sour cream and lemon zest. Gradually stir in flour mixture until a soft, stretchy dough comes together.
Meanwhile, on medium heat, bring large saucepan with 3-in. (8-cm) oil to 180°C (350°F) on an instant read thermometer. Use wet hands to roll heaped teaspoonfuls of dough into balls. Working in batches, place rolled dough onto slotted spoon; place in hot oil. Fry 3 to 4 min., turning once, until golden brown. Transfer fritters to paper towel-lined baking sheet. Make 60 fritters.
Mix cocoa powder and icing sugar. Sift mixture onto fritters to coat. Serve warm or at room temperature.
For a nutty flavour, add 1 tbsp (15 mL) Amaretto or Frangelico liqueur to dough.