In a saucepan on the stovetop add diced onions with 1 tbsp butter. Saute until translucent and golden. Add minced garlic in sauce pan.
Add 2 tbsp butter, allow to melt. Sprinkle in your flour or cornstarch and quickly whisk together until creamy, not allowing it to clump.
Whisk in milk and chicken drippings or broth until smooth. Then add diced fresh basil + a pinch of salt and pepper. Continue to boil so it thickens, taste, adjust seasonings as needed and then remove from stovetop.
Serve immediately. As it cools it will continue to thicken, add more broth to thin out.