Milk Buns with Salted Maple Butter

Name: Milk Buns with Salted Maple Butter
Ingredients: TANGZHONG:; 3 tablespoons (22 grams) bread flour (all-purpose is fine too); 1/2 cup (113 grams) whole milk; DOUGH:; 2 1/4 teaspoons (7 grams) instant dry yeast (see tip); 4 tablespoons (57 grams) unsalted butter, softened; 1/4 cup (49 grams) granulated sugar; 1 large egg; 1 1/2 teaspoons Diamond crystal kosher salt; 2 3/4 cups 2 tablespoons (345 grams) bread flour (divided; all-purpose is fine too); TO ASSEMBLE:; 1 tablespoon whole milk, for brushing; 2 tablespoons (28 grams) butter, melted; 2 tablespoons (39 grams) maple syrup; flakey sea salt