Step 1

Preheat the oven to 350°. Spray a 9-inch round cake pan with baking spray with flour. Line the bottom with parchment; do not spray again.

Step 2

Cut the rhubarb into 2-inch diagonal pieces. Cut each piece in half widthwise so that each piece has a pink side and a green-white side. Place the rhubarb in a large bowl and sprinkle with 2 tablespoons of sugar and the cornstarch. Toss to combine. Place the rhubarb in the prepared pan pink side down, trimming the pieces to fit snugly in the pan.

Step 3

In a medium stainless-steel skillet, melt ¼ cup of butter over medium heat; stir in the brown sugar, honey, and ¼ teaspoon salt. Bring the mixture to a simmer; cook until the sugar is melted and fragrant, about 3 minutes. Slowly pour in the orange juice, whisk until combined and smooth. Pour the caramel over the rhubarb.

Step 4

In the bowl of a stand mixer, beat the remaining ½ cup of butter, remaining 1 cup of granulated sugar, orange zest, and vanilla at medium speed until creamy, 2 to 3 minutes, stopping occasionally to scrape the sides of the bowl. Add the eggs, one at a time, beating well after each addition.

Step 5

In a medium bowl, whisk together the flour, baking powder, ginger, baking soda, and the remaining ½ teaspoon of salt. Gradually add the flour mixture to the butter mixture alternately with the sour cream, beginning and ending with the flour mixture, beating just until combined after each addition. Carefully spread the batter onto the rhubarb in the pan.

Step 6

Bake for 30 minutes. Place a piece of foil on top of the cake to prevent excess browning and bake until a wooden pick comes out clean, 15 to 20 minutes more. Remove the foil and let the cake cool in the pan on a wire rack for 10 minutes. Run a knife around the sides of the cake to loosen; carefully invert the cake onto a serving plate, removing the parchment. Let cool.

Step 7

Serve warm, room temperature, or cold with ice cream or whipped cream.