Melt the butter in a large saucepan over medium heat until it begins to foam. Add the finely minced onion and cook for about five to seven minutes until the onion is soft and translucent. Stir in the minced garlic and cook for just one more minute until it becomes fragrant, being careful not to let it brown too much.
Sprinkle the all-purpose flour over the butter and onion mixture. Use a whisk to combine everything into a thick paste. Continue cooking the roux for about three minutes, stirring constantly. This step is important because it cooks out the raw flour taste and gives the sauce a beautiful golden color.
Slowly pour in the non-alcoholic apple cider while whisking vigorously to prevent any lumps from forming. Once the cider is incorporated, begin adding the broth one cup at a time. Continue whisking throughout this process to ensure the base remains perfectly smooth and consistent.
Bring the mixture to a gentle simmer. Stir in the finely chopped fresh sage, salt, and black pepper. Let the sauce bubble softly for about ten minutes, stirring occasionally, until it has thickened enough to coat the back of a spoon. Taste the sauce and add more salt or pepper if needed to suit your preference.
If you are making this ahead of time, remove the pan from the heat and let it cool to room temperature. Pour the sauce into an airtight container or a glass jar. Place it in the refrigerator until you are ready to use it for your Christmas feast.
