  We modify a three-field formulation of the Poisson problem with Nitsche
approach for approximating Dirichlet boundary conditions. Nitsche approach
allows us to weakly impose Dirichlet boundary condition but still preserves the
optimal convergence. We use the biorthogonal system for efficient numerical
computation and introduce a stabilisation term so that the problem is coercive
on the whole space. Numerical examples are presented to verify the algebraic
formulation of the problem.
