The recipe calls for spraying the oven with water because extra humidity makes the outside of the bread crusty. Simply use a spray bottle filled with tap water.
Bring milk to simmer in small saucepan. Add butter and sugar; stir until butter melts. Pour mixture into large bowl. Add 1 cup room-temperature water and cool mixture until lukewarm (85°F to 95°F), about 10 minutes. Add yeast; stir to blend. Stir in olives, thyme and salt. Add 1 cup flour. Using wood spoon, stir until flour is incorporated. Add 3 cups flour, 1 cup at a time, and stir vigorously with wood spoon until incorporated after each addition. If necessary, add up to 1/2 cup more flour until dough is smooth and begins to pull away from sides of bowl. Oil large bowl. Transfer dough to bowl; turn to coat with oil. Cover bowl tightly with plastic wrap. For do-ahead version: Chill dough overnight. For same-day version: Let dough rise in warm draft-free area until doubled in volume, about 45 minutes (do not punch down dough).
Position rack in center of oven and preheat to 500°F. Oil large baking sheet. Turn dough out onto floured work surface (to avoid deflating, do not punch down dough and do not knead dough). Divide dough into 2 equal pieces. Gently form (do not knead) each piece into baguette 15 inches long by 2 1/4 to 2 1/2 inches wide (dough will not be smooth). Transfer baguettes to prepared baking sheet, spacing evenly apart. Cover loosely with plastic wrap. Let rise in warm draft-free area until slightly puffed, about 30 minutes for refrigerated dough and 15 minutes for room-temperature dough.
Brush top of each loaf lightly with egg white. Generously spray inside of oven with water (about 8 sprays); immediately place loaves in oven. Bake 10 minutes. Reduce oven temperature to 400°F and continue to bake until loaves are deep golden and sound hollow when tapped, about 35 minutes. Cool on rack.