For the sauce, in a medium saucepan over medium-high heat, warm the oil. Add the garlic and cook, stirring, until fragrant, about 1 minute.
In a small bowl, whisk together the shrimp juice and flour until mostly smooth. Add this mixture to the saucepan with the garlic. Cook over medium-high heat, whisking, until slightly thickened and smooth, 3 to 5 minutes.