In the bowl of a stand mixer or a large mixing bowl, dissolve yeast in 1 cup warm water (110°), about 5 minutes.
Add table salt, olive oil, and 1 1/2 cups flour. Beat with a paddle attachment at medium speed or a wooden spoon until dough is stretchy, 1 to 2 minutes. Mix in enough additional flour to make a soft dough, a little more than 1 cup. Knead with a dough hook, or by hand on a floured work surface, adding flour as needed to prevent sticking, until dough is smooth, springy, and no longer sticky, 8 to 12 minutes.
Sprinkle a 10-in.-square work surface with 1/4 cup flour and turn dough out onto it. Pat dough into an even 6-in. square. Loosely cover with a towel and let stand until puffy, 45 to 50 minutes.
Preheat oven to 350°. Line 2 rimmed baking sheets (each 12 by 17 in.) with parchment paper. With a sharp knife, cut dough vertically into 4 strips. Working with 1 quarter at a time, cut vertically again into 8 pieces, sprinkling knife with flour if dough sticks. Pick up 1 piece and stretch it to the length of the pan, then set in pan. Repeat with remaining pieces, arranging them slightly apart.
Gently brush breadsticks with egg to coat, then sprinkle with sel gris and pepper.
Bake breadsticks until golden and crisp in thickest parts, 45 to 50 minutes; halfway through, gently separate any stuck-together breadsticks, and switch pan positions if using 1 oven.
Note: Nutritional analysis is per 2-breadstick serving.