1: Preheat the oven to 180°C/Fan 160°C/Gas 4. Lightly grease a 25cm square cake tin with butter and line the base and sides with non-stick baking parchment, letting some overhang the sides of the tin, to make it easier to lift out the cake later.
2: Put the ﬂour, baking powder and salt into a large bowl and mix well, using a balloon whisk, to combine. Stir in the pistachios, 100g of the chocolate and the sesame seeds.
3: Melt the butter in a large saucepan over a very low heat, then add the demerara sugar, rapeseed and sesame oil, and the eggs. Using the point of a small, sharp knife, scrape out the seeds from the vanilla pod directly into the pan. Heat very gently for 3–4 minutes, whisking constantly, to combine and warm through – don’t overheat or the eggs will curdle.
4: Pour the warm mixture onto the dry ingredients and whisk until thoroughly combined and the chocolate has melted. Finally, fold in the remaining chopped chocolate.
5: Pour the cake batter into the prepared cake tin and bake for 25–30 minutes, until cooked through. It should be lightly golden and quite ﬁrm to the touch. If a skewer inserted into the centre comes up slightly tacky that’s ﬁne, as it means the blondie will be nice and moist in the centre.
6: Remove from the oven and sprinkle on a generous pinch of ﬂaky sea salt. Leave in the tin for 10 minutes, then lift out, peel away the parchment and place on a wire rack to cool.
7: Cut into squares to serve. The blondies will keep for 4–5 days in an airtight tin.