Step 1 In a large, heavy-bottom saucepan, melt the butter over high heat and add the garlic and squash. Cook until the garlic is aromatic, then add the white wine and onion and reduce the heat to medium-low. Cook until the squash is tender and the white wine reduces to a glaze, about 15 minutes.
Step 2 Stir in the broth, cream and thyme and cook until the liquid reduces by one-third, 6 to 8 minutes. Remove from heat, remove and discard the thyme and puree the sauce.
Step 3Strain the sauce and place it back in the saucepan. Season to taste with salt and pepper and thin if desired with additional broth. Set the sauce aside in a warm place. This makes about 2 cups sauce, more than is needed for the remainder of the recipe. The sauce will keep up to a few days, refrigerated (heat before serving).