Start: Heat butter in a large pan over medium-low. Add onions, garlic, and pinch of salt.
Boost Browning: Sprinkle baking soda evenly over onions. Stir well to coat.
Caramelize: Cook for 15–20 minutes, stirring occasionally, until onions are deep golden and garlic is soft. If browning too fast, lower heat and add a little water to loosen. Finish it with a splash of sherry vinegar. Cool and roughly chop.
Mix Dip: In a bowl, combine sour cream and mayonnaise until smooth.
Finish: Stir in onion-garlic mix, onion powder, salt, and sugar. Adjust seasoning.
Rest: Chill at least 1 hour before serving.
Garnish: Sprinkle chopped chives and garnish with a spoon of chilli crisp.