Rhubarb Crumb Cake

rhubarb (about 3 stalks), halved lengthwise and cut into 3-inch pieces

granulated sugar

unbleached all-purpose flour, plus more for pan

light-brown sugar

kosher salt

cold unsalted butter, cut into small pieces, plus 6 tablespoons room-temperature butter, and more for pan

baking powder

large eggs, room temperature

sour cream, room temperature

grated orange zest

heavy cream