Lightly spray an 8½x4½-inch loaf pan with baking spray with flour. Line pan with parchment paper, letting excess extend over sides of pan.
Turn out Essential Brioche Dough onto a lightly floured surface, and divide into 3 portions (about 217 grams each). Roll each portion into a rope about 14 inches long. Pinch ropes together at one end, and carefully braid together tightly. Pinch ends to seal. Place braid in prepared pan, compressing to fit as needed. (Try not to fold the dough too much under itself; this will result in an irregular bumpy top.) Cover and let rise in a warm, draft-free place (75°F/24°C) until puffed and dough passes the finger dent test, 50 to 55 minutes. (See Note.)
Preheat oven to 350°F (180°C).
In a small bowl, whisk together egg and 1 tablespoon (15 grams) water. Lightly brush egg wash over surface of dough.
Bake until golden brown and an instant-read thermometer inserted in center registers 190°F (88°C), 40 to 45 minutes, covering with foil during final 15 minutes of baking to prevent excess browning. Let cool in pan for 10 minutes. Remove from pan, and let cool completely on a wire rack.
Recipe by Bake from Scratch at https://staging.bakefromscratch.com/strawberry-bostock/