Bring the broth to a boil in a large saucepan. Add the green beans and cook until just bright green and crisp-tender, about 3 minutes. Transfer to a bowl with a slotted spoon. Reduce the heat under the broth to low to keep steaming.
Melt the butter in a large saucepot over medium-high heat. Add the onion and a pinch of salt. Cook, stirring occasionally, until almost translucent, about 3 minutes. Add the rice and cook, stirring, until evenly coated and very lightly toasted, about 2 minutes. Add the wine and boil until all the liquid evaporates.
Add 1 cup of the hot broth and cook, stirring, until all the liquid is absorbed. Repeat with the remaining broth, stirring continuously, adding 1 cup at a time, and letting each addition absorb before adding the next. The whole process will take about 30 minutes, at which point, the rice should be just tender.
Remove from the heat and fold in the pesto until evenly distributed. Season to taste with salt. Immediately divide among serving bowls and top with a dollop of mascarpone, baby kale leaves, and shaved Parmesan. Serve hot.