Peel rhubarb. Cut into ¼-inch slices.
Place in a mixing bowl with sugar. Set aside for 1 hour.
In a mixing bowl, combine almonds, sugar, cornstarch, sour cream, egg yolk, cognac and vanilla.
Drain rhubarb, press to remove liquid, and blend into custard mixture.
Preheat oven to 400 degrees.
Cut phyllo leaves across in halves. Place one sheet on a buttered baking sheet.
Brush with melted butter. Repeat and stack 2 more sheets. Spoon rhubarb over phyllo, leaving 1-inch border unfilled.
Brush the edge of pastry with egg yolk. Cover with 3 more buttered sheets of phyllo.
Trim off the pastry edges, leaving a neat 8-to-10 inch circle.
Use a dinner plate as guide. Use left over pastry to form leaves and decorate top of pastry.
Brush leaves, but not the pastry. Use the back of a small knife to trace leaf "veins".
Bake until the pastry is golden brown, about 20 minutes. Remove from the oven and cool.
To make the strawberry sauce:
Puree strawberries, lemon juice and sugar in a blender. Strain.