It is popular sweets in Japan. Recently getting more popular than when I was kid.
It is not popular sweets in U.S. and I can not find any shops and stores. I don’t think American people know about Rusk. So this is the explanation from Wikipedia.
A rusk is a hard, dry biscuit or a twice-baked bread. It is sometimes used as a baby teething food. In the UK, the name also refers to a wheat-based food additive.
German ZwiebackThe zwieback (lit. baked twice) is a form of rusk eaten in Germany.
 GreeceThe term paximadi (Greek: παξιμάδι) covers various forms of Greek rusk, made commonly from barley or chickpea flour, and softened with wine, water or oil before eating. Paximadi form the basis of the Cretan snack dakos (Greek: ντάκος).
 India, Pakistan and South AfricaIn India, Pakistan and South Africa, rusk is a traditional biscuit (also “Khasta” in Hindi, and beskuit in Afrikaans) that is eaten after having been dipped in coffee, tea, or rooibos tea. Historically, rusks evolved (along with biltong) during the latter country’s early pioneering days as a way to preserve bread in the dry climate. It was also extensively used during times of war or when traveling long distances.
Traditionally baked at home, but there are now several mass-market versions available, the most famous probably being Ouma Rusks. Many bakeries, delis and home industries sell them, often using more exotic ingredients than their mass-market counterparts. In addition to plain and buttermilk flavours, there are aniseed, wholewheat, condensed milk, muesli, and lemon poppyseed versions.
If you want to read more, go to this page.
French bread slice 1/3 inch —————————————–12 peaces
Sugar ————————————————————-1 1/2Tbs
Slice bread and put on the baking pan and 238F heated oven for 8 to 15 min.
While you put bread in the overn, mix butter and sugar together and put in the microwave for 20 second.
Mix well this butter and sugar. Put this butter and sugar on the baked bread – one side – and put back in the oven again for 15 min.
After you take off from oven, put sugar on the top of the rusk bread.
It is very easy, you can easily make this! Faster than baking cookies!!