Pile the onions and garlic in the centre of a roasting pan. Cover with the chicken parts. Roast, uncovered, until the chicken is golden brown and caramelized, 30 minutes or so. Carefully pour off accumulated fat, reserving for another use. Transfer the chicken, onions, and garlic to a large saucepan. Pour the apple cider into the roasting pan and stir to dissolve all the browned bits. Pour into the saucepan. Add the soy sauce, brown sugar, cinnamon, bay leaves, peppercorns, allspice, and cloves. Bring to a slow, steady simmer, cover tightly, and cook until thickened and deeply infused with colour and flavour, 45 minutes. Remove the lid, increase the heat, and quickly reduce the sauce, thickening it to 2 cups (500 mL) or so. Remove from the heat and let sit until cool enough to handle. Pour through a fine-mesh strainer into a heatproof container. Refrigerate until cold and firm. Before using, remove any fat that congeals on the surface. The tare can be made 5 days before you need it.