For the burnt grain dumplings, place the flours in a mixing bowl. Make an indentation in the centre, gradually add the water and knead to create a soft and smooth dough. Add the oil and continue kneading. Shape the dough into a ball, wrap in cling film and leave to rest for 15 minutes.
Dust a work surface with durum flour. Take a small piece of dough and roll into a rope shape that is about 2.5cm/1in wide, keeping the rest of the dough wrapped in the cling film. Cut the rope into 1cm/½ in pieces and shape each piece into a shell. Repeat with the rest of the dough. Place the dumplings on a floured board and leave to rest for a few hours or overnight.
Preheat the oven to 200C/180C Fan/Gas 6. Put the onions on a baking tray and bake for 35–45 minutes, or until the sugar in the onions starts to bubble from the root ends. Leave to cool and then peel. Cut in half lengthways and separate the layers into petals. Set aside and keep warm.
Blanch the leeks by placing them roots-end down in salted boiling water for 30 seconds. Preheat a griddle pan over a medium heat and cut the leeks into thick slices. Char-grill the leeks for 6–8 minutes, or until lightly charred. Set aside and keep warm.
For the burnt garlic oil, add the vegetable oil and garlic to a small saucepan and cook over medium–low heat, stirring, until it starts to brown. Reduce the heat to low and continue to cook, stirring frequently, for 10 minutes, or until the garlic turns completely black (the garlic will become very sticky in the process). Transfer the mixture to a heatproof bowl and stir in the sesame oil. Place in a blender and blitz at high speed for about 30 seconds, or until completely smooth. Strain the mixture through a coffee filter or damp muslin and transfer to a sealable container. Use this oil in Step 6 below and the remainder can be stored in the fridge for up to 2 months.
For the garlic dressing, whisk the elderflower vinegar with 4 tablespoons of the burnt garlic oil that was made in Step 5.
Fry the breadcrumbs in the butter with the garlic clove for a few minutes until golden. Discard the garlic. Cook the dumplings in boiling, salted water for 3–8 minutes. Mix the onions, leeks and dumplings with the garlic dressing in a bowl. Season with salt.
Divide the curd cheese between four plates and scatter with the lemon zest. Spoon the leek and dumpling mixture over the top. Cover with the breadcrumbs, hard cheese, nigella seeds and garlic leaves.