Chop the rhubarb into 1-inch long chunks and place in a large bowl. Stir in 1/2 cup of the sugar and set aside for 30 minutes, stirring occasionally. A syrup should form.

Drain the rhubarb, being certain to reserve the syrup for the strawberries (see above) or other uses, like mixed drinks.

While the rhubarb is macerating, butter a 9 inch round pan with at least 2 inch high sides. Place a round of parchment paper cut to fit the pan in the bottom and butter it.

Heat the 1 1/2 tablespoons of butter in a large skillet over medium high heat. When it is melted, add the rhubarb and the remaining 1/4 cup sugar. Stir occasionally--you want the rhubarb to caramelize at the edges but not become mushy. Greenspan estimates about 3 minutes for the job, and that was enough for me.

Scrape the rhubarb with all of its caramelizing juices into the prepared cake pan. Set aside to cool a bit while you prepare the cake.

Preheat the oven to 350 F.

Line a baking sheet with parchment paper.

Whisk together the flour, baking powder and salt.

In a separate large bowl, whisk together the eggs and brown sugar until thick and smooth. Whisk in the orange zest and vanilla.

Whisk the butter in in 3 additions, being sure to scrape sides and bottom of bowl as you go. Then add the flour mixture in 3 additions--whisk for the first 2 additions, but switch to a silicone spatula and fold in the 3rd addition of flour. Be sure that no streaks of flour remain and that the sides and bottom of the bowl are scraped.

Scrape the batter into the cake pan over the rhubarb; make sure the top is level. Place the cake pan onto the prepared baking sheet, and place in the oven.

Bake the cake for 25 minutes, rotating after 12 minutes. When the cake is done, it should be golden brown, pulling away from the sides of the pan, and a cake tester inserted into the center of the cake should come out clean.

Place a large, flat plate by your work area (I used a cake dish, it was definitely trickier but plausible).

Transfer the cooked cake to a cooling rack for 2 minutes, then use a table knife to gently run around the sides of the cake to loosen it from the pan. Place the plate over the cake pan and carefully and quickly flip it over. Now wait 1 minute--you want steam and gravity to help do some of the work. Then remove the cake pan and gently remove the parchment paper--if a few pieces of rhubarb stick (none of mine did), just grab them and place them back on top of the cake.

For the glaze, bring the jam and the water to a boil in a small saucepan. Turn off the heat, and once the bubbling subsides, spoon small amounts of the glaze over the rhubarb topping.

Set aside the cake to cool.

Serve slices with Rhubarb-Sugar Marinated Strawberries and lightly sweetened whipped cream.