Using a sharp knife, trim kale, separating leaves from stems and center ribs. Discard parts of stem wider than 1/4 inch. Coarsely chop leaves and tender stems, placing them in separate piles.

In a large saucepan over medium heat, heat oil until shimmery. Add kale stems and garlic. Cook, stirring often, for about 1 minute, until softened. Stir in salt and pepper. Add kale leaves. Cook, stirring often, for 1 to 2 minutes, until coated and slightly wilted. Pour in stock. Cover, reduce heat to medium low and cook, stirring occasionally, for about 10 minutes, until kale is tender-crisp and stock has evaporated. Drizzle with vinegar to taste. Serve warm.

Variations: drizzle the kale with lemon juice instead of vinegar. Scatter toasted nuts, such as pecans or walnuts, overtop.