Thinly slice both sweet onions into even strips.
Heat 1 tablespoon of salted butter and 1 tablespoon of olive oil in a large skillet over medium heat.
Add the sliced onions, brown sugar, dried thyme, and Kinder's The Blend seasoning to taste.
Stir to coat the onions evenly in the butter, oil, and seasonings.
Cook for approximately 15 minutes, stirring occasionally, until the onions become soft, golden brown, and deeply caramelized. Reduce the heat if they begin browning too quickly.
Add up to ¼ cup of water as needed during cooking to help soften the onions and loosen any browned bits from the bottom of the skillet. Allow the water to evaporate as the onions continue cooking.
Once the onions are caramelized, add a splash of sherry wine to deglaze the skillet, scraping up all the flavorful browned bits.
Cook for another 1–2 minutes until most of the liquid has evaporated.
Remove from the heat and set aside to cool slightly.