Make the dough first. If you are using bread flour or vital wheat gluten, then your dough will be tougher to knead so if you have a machine you can use, I would say go ahead and use it. Me, I always take the easier way out provided I get good results. If you’re doing this by hand, just adapt the instructions to that.
Put the yeast, sugar, salt and flour in the food processor bowl. Pulse a couple of times to mix and then add the warm water in a steady stream. Knead until the dough comes together as a mass and then let the dough rest for 10 minutes. This will help the dough absorb water. Knead again, adding a little more water or flour (not too much) if you need it, until your dough is smooth and elastic but not sticky.
Shape it into a ball and put it in a well-oiled bowl, turning the dough till it is well coated. Cover and let it rise till about double. This should take about 2 hours. If you’re not making the Bialys right away, you can refrigerate the dough overnight at this point. When ready to make them, keep the dough at room temperature for about half an hour and then proceed with the rest of the recipe.
In the meanwhile, make the filling. Heat the oil in a pan, and add the cumin seeds. When the crackle, add the onions, and sauté over low to medium heat. Sprinkle a little salt and continue sautéing until they become soft and turn golden brown in colour. Add the garam masala and stir well. Keep the caramelised onions aside to cool.
Sprinkle your work surface lightly with flour and place the dough on it. Divide it into 8 equal pieces and shape each one into a roll by flattening it and then pinching the ends together to form a smooth ball. Place the rolls on a lightly greased baking sheet and cover them with a towel. Let them rise for about one hour (about 1 1/2 to 2 hours for refrigerated dough) till pressing with a finger on the top leaves a dent.
Work on one piece at a time, while you keep the others covered so they don’t dry out. When the rolls are ready, pick them up one at a time and using your fingers, form the depression in the middle. Hold the roll like a steering wheel with your thumbs in the middle and your fingers around the edges. Pinch the dough between your thumb and fingers, rotating as you go and gradually making the depression wider without actually poking a hole through.
Remember not to press on the edges, or they will flatten out. Once shaped, you should have a depression about 3” in diameter with 1” of puffy dough around the edge, so your Bialy should be about 4” in diameter. Prick the centre of the Bialy with a fork so the centre doesn’t rise when baking.
Place the shaped dough on a parchment lined (or greased) baking tray leaving about 2 inches space between them. Place the caramelized onion filling in the depressions of each Bialy. Brush the outer dough circle with milk.
Bake the Bialys at 450F for about 15 minutes till they’re golden brown in colour. Cool them on a rack. Serve slightly warm or at room temperature. Bialys keep well in an airtight container for a day or two and just need to be warmed up slightly before serving.