Place flour, confectioners’ sugar, and margarine into the bowl of a food processor fitted with a metal blade. Process for 10 seconds, until the mixture resembles sand. Add the egg yolk, water, and vanilla, and process until the dough just comes together.

Mix as little as you need to for the dough to come together.

Place dough on a large piece of plastic wrap. Cover with the plastic and then flatten. Chill in the freezer for two hours or overnight.

Remove dough from the freezer, and let sit at room temperature just until it softens a little so it can be rolled.

Preheat oven to 350 degrees Fahrenheit. Using a little margarine, grease an 8- or 9-inch tart ring, with or without a removable bottom, and place on parchment on a cookie sheet. 

Place a large piece of Gefen Parchment Paper or plastic wrap on your work surface and sprinkle with flour. Place the dough on top, sprinkle with some more flour, and cover with another piece of parchment paper.

Roll on top of the parchment to roll out the dough until it is at least one inch larger than the tart ring. You will want to peel back the parchment and sprinkle some more flour on the dough two to three times while you are rolling.

Gently place rolled dough in tart ring. Cover with foil and weigh the crust down lightly. Bake for 20-25 minutes, or until the crust has colored when you lift up the foil/weights to take a peek.

Lift up the edges of the foil to remove foil and weights, and bake another 5 minutes. Remove ring and allow to cool.

Place the eggs, yolks, and sugar into a heatproof bowl, and set over a medium saucepan with simmering water (a double boiler). Add the lemon juice and zest to the bowl, whisking occasionally until a thick mixture is formed. This takes approximately 25 minutes. Be patient and do not stir too much. Don’t leave the whisk in the bowl with the lemon mixture while it cooks; it may get too hot to touch. If the water in the saucepan boils too fast, turn down the heat. 

Remove bowl from the heat and whisk in the margarine a tablespoonful at a time. Cool for 10 minutes and then cover with plastic and refrigerate eight hours or overnight.

Whip the non-dairy topping until stiff. Fold into the chilled lemon cream. 

Spread into the tart shell. You can place the berries in any design on top of the lemon mousse.

One method is to start at the outside of the tart and place the berries in concentric circles around the cream until it is completely covered. You can place them overlapping or next to each other, as you like. Dust with powdered sugar, if desired.

Chill in the fridge for at least one hour before serving. Store no longer than two days in the fridge.