Preheat the oven to 350°F (175°C).

For the cauliflower crust, remove the outer leaves from the cauliflower and coarsely chop the remaining parts.

Boil for 15 minutes until tender.

Place the boiled cauliflower pieces in a food processor with the chopped garlic and process until finely chopped.

In a bowl, combine the processed cauliflower, egg, sharp cheddar cheese, salt, pepper, rosemary, and mix well.

Press the cauliflower mixture into a nonstick pie plate, shaping it into a crust.

Bake in the preheated oven for 15 minutes.

Meanwhile, prepare the quiche filling.

Sauté the leeks and spinach in a pan for a few minutes until softened.

Set aside.

In a separate bowl, whisk together the eggs and heavy cream.

Stir in the grated Gruyere cheese, chopped chives, salt, and pepper.

Remove the partially baked cauliflower crust from the oven.

Spread the sautéed leeks and spinach evenly over the crust.

Pour the egg and cheese mixture over the vegetables in the crust.

Return the quiche to the oven and bake for about 40 minutes, or until the eggs are set and the top is golden brown.

Once cooked, remove the quiche from the oven and let it cool for a few minutes before slicing and serving.