2 small shallots, sliced into rings
6 tablespoons vegetable oil
1 bunch collard greens (about 10 oz.), center ribs and stems removed, thinly sliced crosswise
6 small radishes, trimmed, sliced
2 tablespoons white wine vinegar
Freshly ground black pepper
Cook shallots and oil in a small saucepan over medium-high heat, stirring occasionally, until shallots are golden, 8–10 minutes. Using a slotted spoon, transfer shallots to a paper towel–lined plate; season with salt. Transfer oil to a small bowl and let cool.
Combine collard greens, radishes, and vinegar in a large bowl; season with salt and pepper. Drizzle with shallot oil and toss to coat. Top with crispy shallots.
DO AHEAD: Crispy shallots can be made 2 hours ahead. Store shallots and oil separately at room temperature.