How did Horace De Saussure make the solar oven?

It was Horace Benedict de Saussure, and not Horace De Saussure, who created the first documented solar oven in 1767 when he used an insulated box with three layers of glass for cooking food and boiling water during one of his many scientific ascents into the Alps around Geneva, Switzerland. This box became widely known as the "de Saussure box."