Melt the butter and vegetable oil in a saucepan over medium heat. Stir in the ginger, and cook for five minutes. Sprinkle in the flour, turmeric, and pepper; stir for 1 minute. Whisk in water and milk. Increase heat to medium-high, and bring to a simmer. Simmer for 3 minutes whisking constantly as the mixture thickens. Season to taste with salt, and strain through a mesh sieve before serving.