In a small saucepan, whisk together milk and flour. Cook over medium-low heat, whisking constantly, until thickened, an instant-read thermometer registers 149°F (65°C), and whisk leaves lines on bottom of pan. Transfer to a small bowl, and let cool completely before using.
Recipe by Bake from Scratch at https://staging.bakefromscratch.com/bake-merry-bright-red-star-yeast/