Slice the gooseberries into rounds and toss with the agave and salt. Soak, covered, in the refrigerator overnight.

Soak the walnut in water overnight.

To prepare the tarts, preheat oven to 375 degrees.

Grease the bottoms of one dozen muffin tins.

Roll out the pastry dough and cut into twelve 2 to 2 1/2-inch rounds. Press the dough circles into the bottoms of the muffin tins.

Bake for five minutes.

While the tart shells are baking, blend the walnuts with just enough water to make a thick walnut cream.

Remove the tart shells from the oven and cool slightly before spreading a dab of walnut cream at the bottom of each tart.

Layer the gooseberries on top of the tart shells, starting from the outside and making a snail pattern inward. Top with any remaining gooseberry liquid.

Bake for 10 minutes or until edges of crust are golden.

Cool slightly before removing from the muffin tins.