Hidden beneath the brown-sugar-crusted custard is the tart, rosy rhubarb purée, an excellent twist on a French classic dessert.
In small saucepan, combine rhubarb, sugar, brown sugar and water; bring to a boil. Reduce heat and simmer for about 10 minutes, stirring occasionally, until thickened and rhubarb is softened. Let cool.
Custard: In saucepan, heat cream to almost simmer. In bowl, stir together egg yolks, eggs and granulated sugar, just until blended; gradually stir in hot cream. Strain through fine sieve into bowl. Stir in vanilla.
Divide rhubarb purée evenly among six 6 oz (175 mL) ramekins or custard cups. Carefully spoon custard mixture over rhubarb.
Set ramekins in large roasting pan and place pan in oven. Pour in enough hot tap water into pan to come halfway up sides of ramekins. Bake in 300°F (150°C) oven, until custard sets but still quivers when gently shaken, about 1 hour. Carefully remove cups from water bath. Let cool on rack to room temperature. Cover each ramekin tightly with plastic wrap and refrigerate for at least 6 hours or up to 2 days.
To Serve: Gently blot any liquid that has formed on surface of custards with paper towels. Sprinkle 2 tsp (10 mL) brown sugar evenly over top of each. Transfer cups to baking sheet. Broil as close as possible to heat source until sugar melts and caramelizes, about 2 minutes. Let stand until sugar hardens. (Desserts may be refrigerated for up to 1 hour after broiling.)