Prepare the filling: Sauté grated apples with butter, sugar, and cinnamon until thickened. Cool.

Make the dough: Mix egg, sugar, and sour cream. Combine flour, baking powder, salt, and vanilla. Cut cold butter into the dry mix, then combine with wet ingredients. Chill dough for 15 minutes.

Assemble: Roll out dough and cut circles. Press into greased muffin tins, fill with apple mixture, and sprinkle with walnuts.

Bake: At 350°F (180°C) for 20-25 minutes, until golden brown.