twice cooked biscuits go by two common names in US, biscotti, (which is a 'cookie') made like a sweet biscuit, (take a basic biscuit dough, add some extra sugar and fat(butter, oil or just shortning)but not to much, flavor (almold or anise) and some chopped nuts (almonds, hazel or pine nuts) shape not into servings sizes, but into a loaf, bake till done. cool, then slice into thick (1/2 to 3/4 inch thick) slices, and bake again in a slow oven (250ºF or so) oven for 30 minutes till crisp)
biscotti are (were) italian cookies, and only available in specialty stores until the coffee craze hit america. nowdays, they are common at starbucks, and other coffee chains, and even grocery stores (they are also easy to make at home)

the other common twice baked cookie is a babies 'zwieback' (or is it zweiback? one of those!) which is almost the same shape as a biscotti, (about 5 inches on bottom, and 1 inch high) but zwieback are more breadlike, and drier.
they were common for teething babies to gnaw on. (in times past!)

there are also rusks (i think that is the english term for zwieback) but its rarely seen in this country.
(and Zed, my local store sells hobnobs, alas, not the chocolate covered ones, but i think chocolate covered 'digestive biscuits' are one of the UK's great culinary contributions!)

and Dr Bill, what we would call a biscuit in US, the english would call a shortbread, or a scone. to them a biscuit is harder, and flatter, (more like what we call a cookie)