1. In a large bowl mix boiling water, butter, sugar, and salt and cool to room temperature. Set aside. Sprinkle yeast over warm water and let stand 5 minutes, until yeast is bubbly. Add yeast mixture to water mixture. Beat in 1-1/2 cups flour. Stir in egg whites, then remaining flour.
2. Grease a large bowl. On a lightly floured surface, knead dough until elastic, 8 minutes. Gather dough into a ball and place in prepared bowl, turning to grease top. Cover bowl and let rise in a warm, draft-free place until doubled in bulk, about 1 hour.
3. Heat oven to 400 degree F. Lightly grease two large cookie sheets. Punch dough down, then knead gently, 2 minutes. Divide dough in half. Roll one portion into a rectangle about 15 minutes long, 8 inches wide and cut into thirty 8-inch-long strips. Roll lightly with floured hands just enough to round cut edges. Place sticks 1/2 inch apart on prepared sheets (keep remaining dough covered). Cover and let rise until doubled in bulk, about 1/2 hour.
4. Brush sticks with milk, sprinkle with sesame seeds and bake until golden brown, 12 to 15 minutes. Cool on wire racks. Repeat process with remaining dough, milk, and sesame seeds. Makes about 5 dozen bread sticks.