Grease a 9×5-inch loaf pan and a medium bowl with the neutral oil, 1 minute.
Warm the milk and water together until just lukewarm, 95–105°F, 1–2 minutes (do not simmer).
In a large mixing bowl, whisk the bread flour, granulated sugar, instant yeast, and fine sea salt until evenly combined, 30 seconds.
Pour the warm milk mixture into the dry ingredients and mix with a dough hook or sturdy spoon until a shaggy dough forms, 2–3 minutes.
Add the softened unsalted butter and knead until the dough is smooth, elastic, and slightly tacky but not sticky, 8–10 minutes (windowpane or stretches thin without tearing).
Transfer the dough to the greased bowl, turn to coat, cover, and let rise in a warm, draft-free spot until doubled in size, 60–75 minutes.
Lightly flour the work surface, turn out the dough, gently press into an 8×12-inch rectangle, then roll into a tight log from the short side; pinch the seam and tuck the ends under, 2–3 minutes.
Place the log seam-side down in the greased loaf pan, cover, and let rise until the dough crowns about 1 inch above the rim and a gentle poke springs back slowly, 45–60 minutes. Preheat the oven to 350°F (175°C) during the last 20 minutes of this rise.
Bake at 350°F until the top is deep golden and the loaf registers 195–200°F in the center, 30–35 minutes; tent loosely with foil after 20 minutes if browning too quickly.
Remove the loaf from the pan and cool on a wire rack until barely warm before slicing, at least 1 hour.