- 2 thyme sprigs
- 1 bay leaf
- 1 1/2 teaspoons whole black peppercorns
- Pinch of crushed red pepper
- 4 tablespoons unsalted butter
- 4 medium onions, coarsely chopped
- 4 garlic cloves, peeled
- 1 small baking potato, peeled and cut into large dice
- 2 tablespoons dry white wine
- 1 1/2 teaspoons sherry vinegar
- Salt and freshly ground black pepper
- Wrap the thyme, bay leaf, peppercorns and crushed pepper in a piece of cheesecloth and secure with kitchen string. In a medium saucepan, melt the butter. Add the onions, garlic, potato, wine and the herb bundle and bring to a simmer over moderately high heat. Reduce the heat to low, cover and cook until the onions are very soft, about 2 1/2 hours.
- Drain the vegetables, reserving the cooking liquid; discard the herb bundle. Transfer the vegetables to a food processor and puree with 2 tablespoons of the cooking liquid and the vinegar. Pass the puree through a sieve, then transfer to a bowl, season with salt and ground black pepper and serve warm.
The puree can be refrigerated for 2 days. Rewarm over low heat.