Chop nuts. Remove the stems from the tarragon and spinach, put the leaves in a blender. Add peeled garlic and oil. Whisk into a puree.
Transfer the mass from the blender to a bowl, add hard cheese grated on a fine grater, mix thoroughly. In another bowl, mix cream cheese and blue cheese until smooth.
Line a cake tin with olive oil-greased cling film (its edges should hang down from the tin so that they can freely overlap each other). Spread a third of the green cheese mixture over the bottom, sprinkle with half of the nuts.
Top with half of the white cheese mixture; then the remaining two-thirds of the green; then nuts; and on top - the remaining half of the white.
Cover the terrine with the hanging edges of the film and refrigerate for 8 hours. Bring to almost room temperature before serving. Serve with a warm baguette.