Prepare the Onions: Start by peeling and thinly slicing the yellow onions. Don’t rush this step — uniform slices ensure even caramelization.

Heat the Pan: In a large skillet over medium-low heat, add the olive oil and butter. Let the butter melt completely before adding the onions.

Start the Slow Cook: Add the sliced onions to the skillet and stir to coat them evenly in the fat. Spread them out in a single layer as much as possible.

Season and Sweeten: Sprinkle the salt, pepper, and brown sugar over the onions. The brown sugar helps draw out the onions’ natural sweetness and encourages browning.

Low and Slow is Key: Let the onions cook slowly over medium-low heat, stirring occasionally. This process takes time — around 30 to 40 minutes — but it’s essential for developing that deep, golden color and rich flavor.

Add a Finishing Touch (Optional): Once the onions are beautifully caramelized, stir in a splash of balsamic vinegar. This isn’t traditional for all versions, but it adds a tangy balance to the sweetness.

Serve Warm: Pile the warm caramelized onions onto freshly grilled hot dogs and enjoy. They’re also great stored in the fridge and reheated for leftovers.