In measuring cup, combine the yeast, sugar, and milk and let sit until very foamy, about 10 minutes. Meanwhile, whisk the flour and salt together in a large bowl and create a well in the center.
Add the warm milk & yeast, yogurt, and optional garlic into flour and mix until well-combined.
Stir until a dough is formed, then turn out onto a lightly-floured surface and knead until smooth, about 3-4 minutes.
Transfer the dough to a large, lightly oiled bowl and cover loosely with a damp kitchen towel. Let rise at room temperature until doubled in size, about 1 hour.
Turn the dough out onto a floured surface. Knead briefly into a disc and cut the dough into equal-(golf-ball) sized pieces and roll into a ball.
Heat a large, heavy bottomed skillet over medium heat. Roll each dough ball out until it is about 1/4 inch thick and approximately 6 inches wide.
Place one at a time onto the hot skillet. Cook until large bubbles form on the surface, about 2 minutes. Flip the dough and cook the other side until golden, about 1-2 more minutes.
Brush the first side with garlic butter.
Stack the cooked flat bread on a plate and cover with a towel to keep warm as you cook the remaining pieces.