1 For the filling place a can of condensed milk in a pan of water, making sure it is completely covered. Bring the water to the boil then reduce the heat right down to the lowest setting and simmer for 3 hours. Top up with extra water if it evaporates.
2 Meanwhile, combine the flour, 125g of the sugar and 200g of the butter in a bowl and work between your fingertips until it resembles breadcrumbs. Add the egg yolks, vanilla extract and soured cream and knead together into a smooth dough. Chill in the fridge for 30-45 minutes.
3 Preheat the oven to 180C/Gas Mark 4. Roll out the dough on a lightly-floured surface to a thickness of about 1 cm/½in. Use this to line a greased brownie tin, approximately 24cm/9½ in. Bake in the oven for 15-20 minutes, or until golden. Remove and allow to cool.
4 Meanwhile, in a frying pan (skillet) melt the rest of the butter and sugar together over a low heat, then add the pecans and most of the sea salt. Toast for a few minutes, stirring all the time. Set aside.
5 Once the condensed milk has turned to caramel and cooled to nearly room temperature, open the can and stir a little bit more salt into it, reserving a little bit for the topping. Generously spread the caramel over the cooled base and top with the caramelised pecans. Sprinkle over a little more sea salt before serving.
• Polska: New Polish Cooking by Zuza Zak (Quadrille, £25)
