Low and Slow Zucchini with Caramelized Onions

Low and Slow Zucchini with Caramelized Onions
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This versatile side dish is a winner for zucchini fans and flavorful veggie lovers alike. The long, slow cooking time brings out a remarkable depth of flavor in this typically mild-mannered vegetable. It's hard to imagine a vegetable more synonymous with high summer than zucchini. The mild-flavored, fast-growing squash lends itself to a staggering variety of preparations, which – given its exuberant growth – can only be a good thing. This recipe brings out the natural flavor of the tender squash by cooking it gently until most of its water content evaporates. The concentrated zucchini flavor is complemented rather than overwhelmed by the addition of sweet caramelized onions and tart lemon juice.


  • 4 medium zucchini
  • 1 large red or Spanish onion
  • 4 Tbsp. oil or butter
  • 2 tsp. packed brown sugar or 1 Tbsp. raw granulated sugar
  • ½ tsp. sea salt, or more to taste
  • ½ tsp. freshly ground black pepper, or more to taste
  • 1 small lemon, cut into wedges


  1. Rinse and dry the zucchini, then trim away their stem and blossom ends. Slice the squash into ¼" rounds, keeping the slices as even as possible – use a mandoline slicer if you have one. Peel and halve the onion, then cut it lengthwise into long strips.
  2. Heat two large, heavy-bottomed skillets over burners set to medium. Divide the oil or butter between them, then arrange the squash rounds to fill the two skillets in a single layer. It may be a tight fit initially, but they'll shrink slightly as they cook. Scatter the strips of onion over the top of the zucchini rounds.
  3. Cook for 10-15 minutes until the zucchini are lightly browned on the first side and the onions have softened slightly. Turn the zucchini rounds to the other side, encouraging the onions into the spaces between them with the edges of your spatula. Scatter the sugar evenly over the surface of the squash, season them generously with salt and pepper and reduce the heat to medium-low.
  4. Continue to cook gently for another 25-30 minutes, turning occasionally. Use a corner of your spatula to work the onions out to the cooler edge of the skillet as they caramelize to prevent burning. Depending on your stove, you might also need to rotate the squash slices from the center to the edges so they cook evenly. They're finished when they're deeply golden and very soft but still hold their shape.
  5. Squeeze a lemon wedge over each skillet and season again with salt and pepper if desired. Serve the zucchini hot or at room temperature with the onions mounded over top and additional wedges of lemon on the side for squeezing. The squash make a versatile side dish on their own, or serve them with crusty bread as a light meal. Refrigerate any leftovers.


You can use the same technique with other summer squash, such as yellow crookneck or Asian long squash, or even with Japanese-style eggplants. If you opt for the eggplant you'll need a bit more oil or butter because the eggplant will absorb most of what you start with and only release it gradually back into the pan.

Add fresh herbs such as basil, thyme or fennel fronds to the pan when the zucchini are nearly finished for a brighter appearance and additional flavor.

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