Heat oven to 400°F. Spread the walnuts on a rimmed baking sheet and roast until fragrant and toasted, 6 to 8 minutes; coarsely chop.
Meanwhile, cook the ravioli according to the package directions, drain, and return them to the pot.
In a small saucepan, bring the cream to a simmer. Add the fontina and mascarpone and cook, whisking vigorously, until melted and smooth.
Gently mix the ravioli with the cream mixture, walnuts, ½ teaspoon salt, and ¼ teaspoon pepper. Sprinkle with the chives before serving.