Add your buckwheat to a pan with a cup and a half of water and simmer for 15 minutes until the water is absorbed and it is soft.
In a separate frying pan sauté your celery, onion, garlic, mushrooms and leeks in a knob of butter (or splash of olive oil) until softened, around 5 minutes over a medium heat.
Combine the two pans and stir through your pesto and cream cheese.
Notes
*If any water remains in the buckwheat pan, drain this before adding to mushroom mix.