Begin from the Breche at the top of the Spencer Couloir on the Blaitiere.
Cross beneath the Central and South summits of the Blaitiere on a ledge (both summits can be gained from here). Continue to the Blaitiere-Ciseaux Col along a rock ridge, gain the S summit of the Ciseaux by descending the Envers side and crossing beneath the N summit and climbing a chimney. (Rebuffat's 100 Greatest Routes suggests you can gain the N summit by "making a difficult lasso"). Return towards the Blaitiere until the Ciseaux canbe passed on the Envers side. A rising traverse and chimney will lead you to the summit block of the Fou and a pitch of V on the NE ridge will gain the summit.