Food is brought to a full boil on any heat source, then transferred, still in its pot, into a heavily insulated box (traditionally hay-packed, now often reflective foam) where residual heat finishes the cooking by slow simmer with no further fuel input. Cuts fuel use for simmered/slow-cooked dishes by roughly 20-80% depending on the dish, since none of the heat that would normally escape to reheat a stovetop pot is wasted. Complementary to, not a replacement for, the wood cookstove/rocket stove/solar cooker entries. It's what happens after the initial boil, not an alternative heat source.
Note: Cost, carbon and footprint are rated against the other options for this same need, not in absolute terms.
No sizing or quantities: how much a technique yields, and how much a household needs, both depend on the build and the people, so the catalogue compares options rather than dimensioning them. It carries no bill of materials and no build sequence, and it is written for an oceanic, clay-soil climate (Normandy, France). Regulatory notes are indicative and need confirming locally.