Onion Puree

A quick spin in a food processor turns long-languishing onions into a silky puree.
Tie the thyme sprigs with kitchen thread. Melt the butter in a large skillet over medium-high heat; add the olive oil; onion and thyme sprigs, stirring to coat. Sprinkle with salt and reduce heat to medium-low. Cover and cook, stirring occasionally, for 1 hour or until the onion is tender. Discard the thyme sprigs. Strain the onion through a fine-mesh strainer, reserving the liquid for other use. Chop the onion in a food processor for 30-60 seconds or until smooth. Serve immediately.