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