2 medium celery roots (celeriac) with leafy tops
1/4 cup olive oil
3 tablespoons butter
1 1/2 cups chopped leek (white and pale green parts only)
3/4 cup arborio or medium-grain white rice
3 cups (about) low-salt chicken broth
1 cup grated Parmesan cheese, divided
Place 1 1/2 cups (packed) celery root leaves and oil in mini-processor. Blend until leaves are minced. Season pesto to taste with salt and pepper.
Peel celery roots. Cut into 1/3-inch-thick slices. Cut slices into enough 1/3-inch cubes to measure 2 cups. Melt butter in heavy large saucepan over medium-low heat. Stir in celery root cubes and leek. Cover; cook until celery root is tender but not brown, stirring often, about 10 minutes. Mix in rice; stir 1 minute. Add broth; increase heat and bring to boil. Reduce heat and simmer until rice is tender and risotto is creamy, stirring occasionally, about 20 minutes. Mix in 3/4 cup cheese. Season risotto to taste with salt and pepper.
Divide risotto between bowls; swirl some pesto on top. Serve with remaining cheese and pesto.