In a large skillet, heat the olive oil, two turns of the pan, over medium-high. Add the onion, celery, chile and garlic; season with salt and pepper. Cook, stirring often, until the vegetables soften, about 5 minutes. Add the passata and 1 cup stock and bring to a bubble. Add the kale and stir until wilted. Simmer, stirring occasionally, until the liquid thickens slightly, about 3 minutes.
In a medium saucepan, bring the remaining 3 cups stock to a simmer over medium-high. Whisk in the polenta, then keep whisking until the polenta thickens, 2 to 3 minutes. Season with the nutmeg, then stir in the mascarpone and Parm; season.
Line bowls with the polenta; make a well in the center of each. Fill with the greens.