Mild and silky-smooth, cauliflower puree lightens up this creamy risotto.
In a medium saucepan, bring broth to a simmer; reduce heat and keep warm.
Meanwhile, in a large heavy-bottomed skillet or pot, heat oil over medium-high. Add shallot and celery, reduce heat to medium, and cook, stirring often, until vegetables are very soft, 10 minutes. Add rice and stir to combine. Increase heat to medium-high and add wine. Cook, stirring, until liquid is almost evaporated, 1 minute.
Add 1/2 cup broth to skillet. Cook, stirring constantly, until broth is almost absorbed. Repeat, gradually adding broth 1/2 cup at a time and stirring constantly, until rice is tender but still al dente and sauce is creamy (you may not need all the broth), 20 to 25 minutes. Add puree and thyme and stir to combine. Remove from heat and season to taste with salt and pepper. Sprinkle with Parmesan and serve immediately.