Flapjacks turn fancy with this yeast batter, which gives them a brioche-like texture.
Heat milk in a small saucepan over medium heat until lukewarm. Transfer milk to a large bowl, and stir in sugar and yeast. Let stand until creamy, about 5 minutes.
Whisk in flour, salt, butter, and egg yolks until batter is smooth. Cover bowl tightly with plastic wrap. Transfer bowl to a warm place; let dough rise until doubled (about 1 1/2 hours), or make batter the night before, and let rise overnight in refrigerator.
Heat griddle to 375 degrees and oven to 175 degrees. Using a 2-ounce (1/4-cup) ladle, pour batter onto griddle, creating several pools, 2 inches apart. Cook pancakes until bubbles form on the top and the edges are slightly dry, about 3 minutes. Using a spatula, flip pancakes; cook until golden on bottom, about 1 1/2 minutes. Transfer to a heatproof plate; keep in warm oven. Repeat with the remaining batter. Serve.