Sauté the onion and rice
Place a large saucepan or pot over medium heat. Add the olive oil and diced onion. Sauté for 5 - 8 minutes or until the onion is softened and translucent, stirring occasionally. Add the rice and sauté for another 5 minutes.
cook the rice
Increase the heat and add the rice. Stir and cook for 2 - 3 minutes. Pour in the wine, and cook for another 2 - 3 minutes for the alcohol to evaporate. Gradually, ladle by ladle, start adding the vegetable stock. Add the next ladle of stock only when the first one is cooked into the rice. Repeat the process until the rice almost cooks. It will take about 15 - 18 minutes. Make sure to stir the risotto regularly.
add the asparagus
Clean the asparagus and chop off the woody parts. Cut half of the asparagus into 0.5 cm (1/4 inch) chunks and add them to the risotto in the last 4 minutes of cooking.
Remove the risotto from the heat and stir in the shredded parmesan cheese and butter. Season to taste with salt and pepper. Cover with a lid and set aside.
Place a skillet over medium heat. Add a teaspoon of olive oil, and the rest of the asparagus cut into 3 cm (1-inch) chunks. Cook for 3 minutes, then lightly season with salt and remove from the heat. Add the lemon juice and stir into the risotto. Sprinkle with grated lemon zest, season with pepper, and serve.