For the dough, combine flour, sugar and baking powder in bowl of food processor. Pulse to mix. Add butter and pulse again until powdery, not sticky. Add eggs and yolk and pulse to form a ball. Divide dough into two unequal pieces, one of which is 2/3 the dough and the other 1/3. Press each into a disk, wrap in plastic and refrigerate.
To prepare filling, combine sugar and 1 teaspoon water in a large saucepan. Stir to distribute water throughout sugar. Place over medium heat and cook, stirring occasionally, until the sugar turns to a deep amber caramel. Off heat, add cream and honey, then return to heat and return to a boil. Boil 1 minute. Stir in walnuts off heat, then pour into a buttered bowl to cool slightly.
Preheat oven to 350 degrees and set a rack in the lower third.
Roll out the larger piece of dough to line the bottom and sides of the pan. Pour in cooled filling and smooth top. Roll remaining dough to a 9-inch disk and slide on top of filling. Ease extra dough from side of pan onto and over top crust to make a border around the edge.
Bake until it is a deep golden color and feels somewhat firm when pressed with a fingertip, about 45 to 55 minutes. Cool in pan on a rack. Wrap tightly in plastic and keep at room temperature about 24 hours before serving.