Clean the celeriac thoroughly, removing the outer peel and the tougher fibrous parts. Then cut the celeriac into fairly small cubes to promote even cooking.

Arrange the cubes on a baking tray lined with parchment paper and cook in a fan oven preheated to 160 °C for about 40–45 minutes, until very tender. Once cooked, transfer to a mixer and blend until smooth and homogeneous.

Pour the purée into a clean kitchen cloth and squeeze thoroughly to remove as much excess water as possible. This step is essential to obtain a compact base: too much moisture would compromise the final texture.

Transfer the well-drained purée to a large bowl.

Add the whole eggs, egg whites, grated pecorino and salt, then mix carefully until the mixture is uniform.

Add the sifted flour and combine until a homogeneous dough is obtained, soft but workable.
 

Line a baking tray with parchment paper.

Spread the mixture to form a disc about 22–24 cm in diameter and approximately 1 cm thick, leveling the surface with the back of a spoon or a spatula.
 

Cooking
Cook in a combi steam oven for 16 minutes. Cook the final 2 minutes in static mode at 200 °C.

Remove the base from the oven and allow it to cool. Distribute the well-drained, torn mozzarella over the surface, ensuring it is dry to prevent excess moisture during cooking.

Return  to the oven for 2–3 minutes, until the mozzarella is fully melted.

Remove from the oven and finish with a drizzle of extra virgin olive oil and freshly chopped herbs to taste (thyme, marjoram or parsley). If desired, add a light final sprinkling of pecorino.

Let rest for a couple of minutes before slicing and serving, so the base can set properly.