Prepare a 9-inch diameter round tart pan, preferably with a removable bottom. Finely grind the cookies in a food processor. Add melted butter and blend well. Spread the mixture on the bottom and sides of the pan and press firmly. Place in the fridge while preparing the next steps.

Wash the strawberries and remove the stems. Place 1½ cups of strawberries in a saucepan and set them over low heat. Cook for about 35 minutes, stirring frequently, until the water evaporates and thickens; they should resemble jam in texture. Add the white chocolate, stir thoroughly, and cook over very low heat for about 2 minutes, until the chocolate melts. Remove from heat and set aside to cool.

When the filling has cooled, transfer it to a blender. Add mascarpone and blend to a perfectly smooth cream. Take the pie crust out of the refrigerator and arrange the strawberry filling on it. Cover the tart tightly and place it back in the refrigerator for at least 4 hours, or preferably overnight. Just before serving, slice the remaining strawberries. Garnish the tart with them and sprinkle with pistachios. Serve immediately.