For hazelnut pastry, process hazelnuts in a food processor until coarsely chopped, add flour and icing sugar, process to combine. Add butter, process until crumbs form, add egg, process to combine. Bring together with the heel of your hand, form into a disc, wrap in plastic wrap, refrigerate to rest (1 hour). Preheat oven to 180C. Roll pastry on a lightly floured surface to 4mm thick, cut a 23cm-diameter round and line base of a 6cm-deep, 23cm-diameter ring mould placed on an oven tray lined with baking paper. Prick with a fork and bake until crisp and golden (10-12 minutes). Reduce oven to 160C.
Meanwhile, simmer sultanas and verjuice in a small saucepan over medium heat until liquid evaporates (5-6 minutes), then set aside to cool. Process ricotta, mascarpone, eggs, honey, icing sugar, rinds and vanilla seeds in a food processor until smooth, then stir through sultanas. Spoon over pastry base, smooth top and bake until golden and set (1-1¼ hours). Cool, refrigerate until chilled.
Meanwhile, for scorched grapes, simmer honey in a frying pan over medium-high heat until caramelised, swirling occasionally (3-4 minutes). Add verjuice, swirl to combine, add grapes, cook until syrupy (5-7 minutes), cool to room temperature.
Transfer torte to a serving plate, remove mould, spoon over grape mixture and serve.