Marinated Rainbow Chard From 'Franny'S'

Remove the stems from the chard leaves. Cut the stems in half lengthwise, then into 3-inch lengths. Keep the leaves whole.
Heat a large skillet over medium-high heat. Add 1/4 cup of the olive oil and the 4 smashed garlic cloves and cook until the garlic is light golden brown, about 2 minutes. Remove and discard the garlic.
Add the stems to the garlic oil and sprinkle with salt. Cook until the stems are browned in spots, 4 to 5 minutes (if the stems begin to brown too much before they are tender, add a few tablespoons of water). When the stems are almost tender, stir in the 2 tablespoons vinegar. Cook until the stems are shiny and tender, 1 to 2 minutes more. Transfer to a platter.
Return the skillet to medium-high heat, add 2 tablespoons olive oil and the 2 chopped garlic cloves, and cook for 1 minute. Add the chili flakes and cook for 30 seconds. Add the chard leaves, season with salt, and cook until wilted, 1 to 2 minutes. Transfer the greens to a plate and let cool.
Place the greens in a bowl and sprinkle with the remaining 2 tablespoons olive oil and 1/2 teaspoon vinegar and the pepper. Gently mix in the stems. Let marinate for at least 20 minutes before serving, or for up to 1 day. Store in the refrigerator if marinating for more than 2 hours.