Heat oven to 400 F with oven rack in lowest postion. Line a sheet pan with foil for easy cleanup.
On a lightly floured counter roll out bottom crust and line a 9 inch pie plate. Shape almond paste into a flat disk. Roll disk between waxed paper to a 9 inch circle. Press into bottom and up sides of pie shell.
Combine sugar , cornstarch , tapioc , cinnamon , nutmeg and salt in a large bowl . Add rhubarb and blueberries. Toss to combine and pour into pie shell. Dot with butter.
Place the top crust to cover pie and crimp edges. Brush top with milk and sprinkle with sugar. Cut 3 or 4 vent holes in top crust and place on baking sheet.
Bake for 25 minutes , then lower temperature to 375°F Bake an additional 25 to 30 minutes or until crust is golden and juices are bubbling. Cool before serving.