Martha Stewart: Rhubarb turns Martha upside down

I HAVE HAD a lifelong relationship with rhubarb (Rheum x cultorum), which began in my father's garden in Nutley, N.J., many years ago.

Rhubarb leaves grow more than a foot in length and contain a toxic amount of oxalic acid, a substance that can cause illness if ingested. The edible stems from which the poisonous leaves sprout are called the petioles, which grow from 14 to 24 inches long.

Cut into half-inch-long pieces and seasoned simply with sugar, the stalks are a delicious way to fill pies, top cakes, make jams, jellies and chutneys, and flavor custards.

I loved getting the directive from my dad to pick 20 stalks for a pie. Picking rhubarb is fun because one pulls the stalks from the plant, each stalk snapping out with a pop.

The leaves have to be cut off and thrown onto the compost piles (they seem to have no ill effects on the safety of compost). After rinsing, the stalks are ready to use.

I grow several varieties of rhubarb, always looking for redder and sweeter types. Two long rows provide plenty of this unusual vegetable to use during the season, plus enough to freeze for later in the year, with some left to share with friends.

Rhubarb has a long history; its cultivation as a medicine to aid digestion is believed to have started around 2700 B.C. in China. In the 17th century, there were rhubarb rhizomes planted in Italy. In the 1800s, it was often used as medicine in France and as both food and medicine in England. In the United States, it was used for drinks and tonics as well as for cooking.

Because rhubarb is very easy to grow and because the plants are readily available, I encourage you to find a place in your garden for it. The rewards in the kitchen will be well worth it.

For more rhubarb recipes, please visit marthastewart.com/rhubarb.

This cake has a crumb "topping" that actually ends up on the bottom. Each bite has a surprisingly crunchy texture.

RHUBARB UPSIDE-DOWN CAKE

For the topping:

4 tablespoons unsalted butter, melted

1/2 cup all-purpose flour

1/4 cup sugar

Coarse salt

For the cake:

1 1/2 sticks unsalted butter, room temperature, plus more for

buttering pan

1 pound rhubarb, trimmed and cut on a very sharp diagonal about

1/2-inch thick

1 3/4 cups sugar

1 1/2 cups all-purpose flour

1 1/2 teaspoons baking powder

Coarse salt

1/2 teaspoon finely grated orange zest plus 1 tablespoon fresh

orange juice

2 large eggs

1 cup sour cream

1. Preheat oven to 350 F. Make the topping: Stir together butter, flour, sugar and 1/4 teaspoon salt until moist and crumbly.

2. Butter a 9-inch round cake pan (2 inches deep). Dot with 4 tablespoons butter (cut into pieces). Toss rhubarb with 3/4 cup sugar; let stand for 2 minutes. Toss again, and spread in pan.

3. Whisk together flour, baking powder and 1 1/2 teaspoons salt. Beat remaining stick butter and cup sugar with a mixer on medium speed until pale and fluffy. Beat in zest and juice. Beat in eggs, 1 at a time, until incorporated, scraping down sides of bowl. Beat in flour mixture in 3 additions, alternating with sour cream, until smooth. Spread evenly over rhubarb. Crumble topping evenly over batter.

4. Bake until a toothpick inserted into the center comes out clean and top springs back when touched, about 1 hour. Let cool for 10 minutes. Run a knife around edge of cake, and invert onto a wire rack. Let cool completely. Serves 10.

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