Thoroughly wash the leeks to remove any dirt, then discard the tough dark green tops. Thinly slice the tender white and light green parts of the leek.
In a medium pot, heat the vegetable stock over medium heat until simmering (you can also heat the stock in a large bowl in the microwave). Remove from the heat and set aside.
In a large nonstick pan, melt the butter with the olive oil over medium-low heat, then add in the shallot, leeks, and garlic. Sauté for about 5 minutes or until soft and fragrant.
Add in the rice and toast, stirring frequently, for 2-3 minutes.
Then add in the white wine to de-glaze the pan and make sure to scrape up any browned bits on the bottom of the pot.
Add in ½ cup of the warmed vegetable stock, thyme, salt and pepper, and stir the risotto until completely absorbed, then add in another ½ cup and repeat. Continue to add in the stock ½ cup at a time until it's all absorbed and the rice is fully cooked.
Stir in the parmesan, spinach, and lemon zest. Then taste and adjust seasonings if desired.
Make sure to read the instructions on the rice you're using and adjust the water as necessary. Most Arborio rice uses a 1:4 rice to water ratio, but some are 1:3.If using store-bought vegetable stock, you may need to reduce the salt.