Grate rind of orange; set aside for pastry. Juice orange.

In saucepan, combine orange juice, rhubarb, sugar and salt. Simmer over medium-low heat until thick and mushy, about 15 minutes. Mix cornstarch with 3 tbsp/45 mL water until dissolved; stir into rhubarb mixture and simmer for 2 minutes. Let cool.

Pastry: In bowl, whisk together flour, sugar, baking powder and salt. In food processor, mix together butter, cream cheese, sour cream, orange rind, vanilla and eggs until smooth. Add flour mixture; process just until dough forms loose ball. On lightly floured surface, knead dough until smooth, about 30 seconds; divide in half and form into 2 discs. (Make-ahead: Refrigerate for up to 1 day; bring to room temperature before using.)

Line 15- x 10-inch/38 x 25 cm rimmed baking sheet with parchment paper. Roll out 1 disc of dough into rectangle large enough to fit bottom of pan plus 1/2 inch/1 cm on each side; fit into bottom and up sides of prepared pan. Spread almonds over dough; cover with rhubarb mixture.

Roll remaining dough out into rectangle about 1/4 inch/5 mm thick. Using pastry wheel, cut into 1-inch/2.5 cm wide strips; arrange in lattice pattern over rhubarb mixture. Mix yolk with milk; brush tops of strips with egg mixture and sprinkle with sugar.

Bake in bottom third of 375F/190C oven until pastry is golden and filling is bubbly, 25 to 30 minutes. Let cool. Cut into squares.

Makes 12 to 16 servings.