Preheat oven to 180C. Blend ricotta, buttermilk, sugar, 50gm butter and egg yolk in a food processor until smooth. Add flour, baking powder, bicarbonate of soda, rind and vanilla, and pulse until dough just comes together. Turn onto a lightly floured surface, knead until just smooth, then roll out to a 30cm x 45cm rectangle and brush with remaining butter.
For cinnamon-cherry filling, combine ingredients, except ricotta, in a bowl, then scatter evenly over dough with the longest edge nearest you, leaving a 3cm border at the edge furthest from you. Scatter ricotta over, then roll away from you to form a tight cylinder. Trim uneven ends, then cut into 13 even pieces and place 6 pieces flat-side down in the base of a buttered 2.25-litre, 22cm-diameter fluted ring tin. Arrange remaining slices on top, offsetting slightly as you go, then bake until risen and golden (30-40 minutes).
For crunchy espresso glaze, whisk ingredients and 1 tbsp warm water in a bowl, drizzle thickly over cake and scatter hazelnuts on top. Allow icing to set (10-15 minutes), then slice and serve.
Note Dried sour cherries are available from
select delicatessens and online at pariya.com.