Rhubarb Upside Down Cake

My mom has always grown a lot of rhubarb in her garden so I grew up with all sorts of foods with rhubarb, rhubarb cake, rhubarb bread, rhubarb pie, but none of them compare to this rhubarb upside down cake. Now that I have a house of my own, I also am growing rhubarb and made my cakes with half my rhubarb and half my mom's. Give it a try!

Rhubarb Upside-Down Cake

Crumb topping:
4 tblsp. Unsalted butter, melted
½ cup all-purpose flour
¼ cup sugar
Coarse salt

For the cake:
1 ½ sticks unsalted butter, room temperature, plus more for buttering pan
1 pound rhubarb, trimmed and cut on a very sharp diagonal, about ½ inch thick
1 ¾ cups sugar
1 ½ cups all-purpose flour
1 ½ teaspoons baking powder
Course salt
½ tsp. finely grated orange zest plus 1 tblsp. Fresh orange juice
2 large eggs
1 cup sour cream

Preheat oven to 350 degrees. Make the topping:
Stir together butter, flour, sugar and ¼ tsp. salt, until moist and crumbly.

Butter a 9-inch round cake pan (I used an iron skillet). Dot with 4 tblsp. Butter, cut into
Pieces. Toss rhubarb with ¾ (or more) cup sugar; let stand for 2 minutes. Toss again, and spread in pan.

Whisk together flour, baking powder and 1 ½ tsp. salt. Beat remaining stick butter and cup sugar with 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.

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