Blanc de Blancs is Champagne made exclusively from the white grape varieties permitted under the Champagne appellation. Chardonnay is by far the most common, but Pinot Gris (aka Fromenteau Gris), Pinot Blanc and Arbane are also sanctioned for use under the appellation laws. That said, only a very small number of producers make Blanc de Blancs Champagne from anything other than Chardonnay; Drappier's Quattuor is the most accessible and is produced from four different white varieties – whence the name.
Not only is it still legal to make Blanc de Blancs champagne from varieties other than Chardonnay, there are further vinous gems to be uncovered. A varietal Petit Meslier champagne is produced by Duval-Leroy, creating an incredibly rare Champagne cuvee containing neither Pinot Noir, Pinot Meunier nor Chardonnay. The tasting notes for this Champagne (thanks to Jancis Robinson for these) tell of a 'green leafy character and a powerful aroma'. Likewise, Champagne house Moutard have produced a varietal Champagne Cepage Arbane.
The style of any Blanc de Blancs is distinct from other Champagnes – most of which are made with high proportions of black-skinned Pinot Noir and Pinot Meunier grapes. Blanc de Blancs means literally 'white of whites' and is thus the exact opposite of Blanc de Noirs. (© All rights reserved, Wine-Searcher.)
Famous examples of Blanc de Blancs Champagnes are Dom Ruinart, Salon Le Mesnil and Krug Clos de Mesnil. The latter two are made entirely from Chardonnay grapes sourced from Mesnil-sur-Oger, a village in the Cote des Blancs sub-region. The Cote des Blancs (literally the Hill of Whites) is located south of Epernay and is essentially a chalky, east-facing slope just under 10 miles (16km) in length.
Almost every other white wine in the world is made from white grapes; it is only due to the particular production techniques used in Champagne that the title Blanc de Blancs is required to distinguish one white wine style from another.