Pie Dough, or your favorite prepared crust (and skip steps 1 and 2)
All-purpose flour, for dusting
1 3/4 pounds (about 6 cups) rhubarb, ends trimmed, cut crosswise into 3/4-inch pieces
1 cup sugar
2 tablespoons cornstarch
Pinch of salt
For the almond crumble:
2/3 cup whole oats, ground to a flour in a food processor (yielding 1/2 cup oat flour)
1/2 cup all-purpose flour
1/2 cup sugar
1/4 teaspoon ground cinnamon
1/2 teaspoon kosher salt or Less regular salt
3/4 cup unsalted whole almonds, coarsely ground in a food processor or chopped medium fine by hand
6 tablespoons unsalted butter, melted and cooled