Updated Apr 4, 2019Chatelaine
- Position rack in bottom third of oven, then preheat to 375F.
- Use a sharp paring knife to slice vanilla bean in half lenthwise. Scrape out vanilla seeds from one half with the dull side of the paring knife. (Reserve the other half for another use.)
- Unroll pastry, then sprinkle over 1 tbsp sugar, rubbing to coat evenly. Transfer, sugar side down, to a large sheet of parchment, then sprinkle top with 1 tbsp sugar, rubbing to coat. Roll pastry into a 10 x 12-in. rectangle. Transfer parchment and pastry to a baking sheet. Freeze until semi-firm, about 15 min. Trim edges with a ruler to make straight sides, if needed. Cut into twelve 2 1/2 x 4-in. rectangles. Prick each piece 5 times with a fork.
- Rub remaining 2/3 cup sugar and vanilla bean with fingertips in a 9 x 13-in. baking dish. Add rhubarb and toss to combine, then arrange in a single layer. Cover tightly with foil.
- Place another sheet of parchment on top of pastry, then top with another baking sheet of the same or smaller size. Weigh down with the baking dish with rhubarb. Bake in bottom third of oven for 20 min. Remove foil and flip rhubarb. Continue baking, uncovered, until rhubarb is tender but still firm, 8 to 10 min.
- Transfer baking dish and pastry to rack to cool completely. Transfer rhubarb to a large plate. Reserve syrup.
- Beat cream in a medium bowl with an electric mixer on medium until stiff peaks form, 3 to 5 min. Beat in 2 tbsp reserved syrup. Taste, then add 1 tbsp more syrup if you prefer it sweeter. Transfer to a piping bag fitted with a 1/2-in. star tip.
- To assemble mille feuilles: Top 4 sheets of pastry with 3 pieces each of the rhubarb, then pipe dots of cream on top of rhubarb. Top each with another sheet of pastry, 3 pieces of the rhubarb and cream. Place remaining sheets of pastry on top. Dust with icing sugar, if desired.
Kitchen Tip: The baking time works for rhubarb stalks about 3/4 in. wide. If you have thinner stalks, reduce baking time by 10 min.
Kitchen Tip: Use the leftover vanilla bean half or empty pod to make your own vanilla extract: Steep chopped vanilla in 1 cup bourbon or vodka. Set aside in the pantry, shaking occasionally, for at least 8 weeks before using.
Kitchen Tip: To make our design, cut a piece of parchment and place it diagonally over the top layer. Dust with icing sugar, then remove parchment.