Prepare an ice-water bath. Bring a large pot of salted water to a boil. Add snap peas and blanch 3 to 4 minutes. Transfer to ice bath; let cool, then drain on a paper towel-lined plate.
Add fava beans to pot and blanch 1 to 2 minutes. Transfer to ice bath and let cool; drain on plate. Pop favas from skins.
Melt butter in a large saute pan over medium. Add favas and cook, stirring occasionally, until crisp-tender, 4 to 5 minutes. Add peas; season with salt and pepper. Cook, stirring occasionally, until tender and heated through, 3 to 5 minutes. Transfer to a serving bowl and sprinkle with mint.
