Add the flour, semolina, salt and sugar in your food processor mixing bowl and mix thoroughly. Then mix the yeast and water in a separate bowl until the yeast is dissolved,  and add it to the flour mixture.

Next, add the olive oil and mix the dough for 2 minutes at a low speed or until there’s no loose flour in the bowl. Knead the dough for another 8 minutes at medium speed, or until the dough is smooth and ceases sticking to the sides of the bowl.

Note: You can also use a spatula to remove the dough from the sides if needed.          

Cover the dough and leave it to rise for 2 hours at room temperature. Alternatively, you can set it in the fridge and leave it to rise overnight. 

Next, roll the sausage meat into walnut-sized balls –– about 1 inch in diameter, or 2 ½ centimeters –– with wet hands to make about 12 balls. Set aside. 

Warm the clarified butter in a frying pan over medium-low heat, then add the onions and sauté until soft, about 10 minutes. Then add the kale and sauté for another 10 minutes, stirring until most of the liquid has evaporated.

Season the mixture with salt, pepper and mustard and leave to cool slightly, then stir in the grated cheese and eggs.

Next, brush a cast-iron skillet pan with oil and preheat your oven to 500°F (260 °C). Use an infrared thermometer to check the oven stone.

On a flour-dusted work surface, divide the dough into 2 equal portions then use a rolling pin to roll them into 10-inch (25-centimeter) rounds. 

Place your pizza dough in your cast-iron skillet and begin to press it evenly into the bottom and up the sides. Leave the dough to rest for 10 minutes.

After resting, place the skillet in your oven and set it toward the back. Let it cook for 5 minutes then turn it halfway and continue cooking until the surface of the pizza is slightly and evenly browned.

Now, take the skillet out of the oven and top the dough with half of the kale mixture and 6 Mett balls. Then place it back in the oven toward the front and continue baking for another 20 minutes, rotating it every few minutes for an even cook. If the top is browning too fast, turn off the oven, move the skillet to the middle and close the oven door to continue baking the pizza in the residual heat.

Take the skillet out of the oven and let the pizza rest for 5 minutes. Then slice it in the pan and serve piping hot.