Place a large saucepan over a medium heat. Add the olive oil and sauté the onions for 5-6 minutes, until beginning to turn translucent. Add the beef and stir through. Cook on all sides until brown all over, about 5 minutes. Add the salt, cumin, coriander and cinnamon and stir through, cooking for a further minute before adding the sieved tomatoes along with ½ cup water. Cook for 10 minutes, stirring every two minutes, until the sauce clings to the meat and no liquid remains. Allow to cool completely.
For the dough, grease 2 x 9” round pans with ghee (you can also use an ovenproof saucepan for this).
Put the yeast in a small bowl and cover with ¼ cup tepid water. Whisk with a fork and allow to stand for 5 minutes, until it becomes frothy.
In a large bowl, sift together the flour and milk powder. Add the yeast water mix and oil then rub together with your fingers until the mixture resembles wet sand.
Whisk together 2 eggs with the remaining cup of water and add to the mixture. Bring together with your hands then tip out onto a floured work surface. Knead for 4-5 minutes, until the dough is smooth. Roll into a ball and put in an oiled bowl covered with a tea towel. Place in a warm place to rise for 45 minutes to rise.
Preheat the oven to 180°C. Divide the dough in half and roll out into 2 x 10-inch circles. Place into the prepared tins and allow the edges to overhang. Spoon the cooled meat mixture into the centre and top with the sliced tomatoes. Fold the edges over the meat mixture.
Whisk together the remaining egg, vinegar and 2 tbsp water together. Brush over the dough and sprinkle over sesame seeds.
Place into the oven for 40-45 minutes, until golden brown and fragrant.
Whisk together the tahini and lemon juice. Drizzle over the pizzas and sprinkle with chives before serving.