This work examines the process of adhesion plaque formation between pairs of copolymer vesicles presenting dense surface concentrations of avidin (NeutrAvidin) and biotin. Micropipet aspiration maintains constant membrane tension, as the low-tension vesicle membrane spreads over a second, more tensed vesicle. Spreading rates near 1 microm/s but as high as 7 microm/s (the adhesion plaque diameter) and contact angle growth rates of 2-14 deg/s are observed. The ultimate contact angles, in the range of 120-140 degrees, are independent of membrane tension and also exceed those previously reported. Adhesion plaque formation occurs in three phases: an initial step in which contact is established, typically lasting from a few seconds to a minute, an abrupt jump into contact in which both vesicles undergo substantial deformation, and a slower continued growth of the contact angle and area. Vesicle pairs are irreversibly bound at the plaque such that attempts to peel them apart cause membrane rupture at critical tensions as high as 4 mN/m, setting a lower bound on the interfacial strength. When the quantity tau(1 - cos theta) (with tau the membrane tension and theta the contact angle) is plotted as a function of time during plaque formation for different values of tau, the curves fail to collapse, indicating the chemical driving force for adhesion greatly exceeds the mechanical resisting tension.