Preheat the oven to 350F. In a medium bowl, combine the oats, flour, brown sugar, cinnamon and salt. Add the butter and blend until crumbly; press into the bottom and sides of a 9-inch pie plate and bake for 15 minutes, or until pale golden.
To make the filling, combine the rhubarb, 3/4 cup of the sugar and the cornstarch in a medium saucepan. If you like, add a splash (a couple tablespoons) of water or orange juice to help get things going. Bring to a simmer and cook, stirring often, until the rhubarb breaks down and the mixture thickens.
Spread the rhubarb in the pie crust and in a medium bowl, whisk together the sour cream, cream, remaining 1/2 cup sugar, eggs, vanilla and salt. Pour over the rhubarb and bake for 30-40 minutes, until the pie is golden and set around the edges, but still a bit wobbly in the middle. Cool, then refrigerate for a few hours, until chilled.