1. Warm your oven to 200°C/Fan 180°C/Gas 6. Peel the onions and slice them into wedges. Break up the garlic bulb but don't peel the cloves. Scatter the onions and garlic into a roasting tin and toss with 1 tbsp olive oil and a pinch of salt and pepper. Slide the tin into the oven and roast for 20 mins. After 20 mins, scoop the garlic cloves out of the roasting tin and set aside for later. Turn the onions and return them to the oven for a further 10-20 mins, till tender and caramelised at the edges. Once cooked, allow the veg to cool, then pop the garlic cloves out of their skins. Finely chop the onions and garlic and set aside.
2. Tip the flour into the mixing bowl for a stand mixer, or a large bowl if you're making the dough by hand. Add 1½ tsp dried yeast, a good pinch of salt, 2 tbsp sugar, 6 tbsp sesame seeds and 1 tbsp caraway seeds (if using), along with the cooked onions and garlic.
3. Pour in 500ml lukewarm water (hand-hot is perfect) and 2 tbsp vinegar and mix to form a dough. Knead the dough with the mixer or your hands for at least 10-15 mins, till the dough is smooth and elastic in texture. Cover the dough in the bowl and set aside for 1½-2 hrs, till doubled in size.
4. Once the dough has risen, divide it into 12 even-sized pieces. Roll each piece on a clean surface till round, then cover the balls on the work surface and allow to prove for a further 20-30 mins.
5. Warm your oven to 220°C/Fan 200°C/Gas 7. Fill a large pan with water and bring to the boil. Once the water in the pan is boiling, stir in 4 tbsp sugar.
6. To shape the bagels, stick a finger into the middle of each piece of dough and carefully stretch outwards, till a 3cm-wide hole is formed. Carefully drop 1-2 bagels into the boiling water, allowing plenty of space in the pan. Poach the bagels for 1 min, then carefully turn them over with a spoon or tongs. Poach for a further 1 min, then transfer the bagels to 1 or 2 large baking trays. Repeat the poaching with the remaining bagels.
7. Once all of the bagels have been poached and are arranged on the baking tray, sprinkle them with a few more sesame seeds. Slide the trays into the oven. Bake the bagels for 20-25 mins, till golden brown and crisp at the edges. Transfer to a rack to cool.
8. These bagels are really good sliced, spread with mustard and topped with salt beef and pickles. They will keep in an airtight tin for 2-3 days, or they can be frozen for up to 3 months.