Rhubarb-Almond Danish Braid

For pastry: In a small bowl, whisk together warm water, yeast and 1/2 teaspoon sugar. Let rest until bubbly, about 5 minutes. Meanwhile, in a large mixing bowl, whisk together all-purpose flour, 3 tablespoons sugar and the kosher salt. Add butter cubes; toss to coat. With a strong thumb, press each cube once against the side of the bowl. Whisk milk and the egg yolk into yeast mixture, then pour over flour mixture. Using a silicone spatula, bring everything together into a rough blob.

Turn dough onto a lightly floured work surface and pat into a square about 1 inch thick. With a lightly dusted rolling pin, roll dough into a long rectangle, about 24×8 inches, with the long side parallel to the counter edge. Using a bench scraper or metal spatula to lift pastry, fold the short sides in so they meet in the middle, then fold the left side over right, as if closing a book. Turn the book spine so it runs parallel to the counter edge; repeat the roll-and-fold. Cut pastry crosswise in half. Wrap each half in plastic. Chill one portion overnight (or up to 4 days); freeze the remaining portion for another braid on another day. (Defrost in refrigerator overnight before using.)

For rhubarb: Preheat oven to 400°. In a parchment-lined 15×10-inch baking sheet, toss together rhubarb and 1/4 cup sugar. Roast until tender (but not falling apart), 15 to 20 minutes. Let cool.

For almond paste: In a small bowl, combine almond flour, 2 tablespoons softened butter, the remaining 1/4 cup sugar, the egg yolk (don't throw away the egg white), almond extract and a pinch of kosher salt; stir vigorously until smooth.

To assemble: On a large parchment sheet, roll out pastry to a 15×10-inch rectangle; transfer pastry on parchment to a large rimmed baking sheet. With the pastry's long side facing you, spread almond paste top to bottom down the middle, leaving 5 inches of pastry bare on each side. Repeat with rhubarb. On both sides, slice the untopped pastry into 8 strips by running a knife from the filling downward on the diagonal. (The top "strip" will look more like a triangle. That's OK.) Working top to bottom, fold strips over filling, alternating sides. Press to seal ends and tuck under. Let rise 30 minutes. (It won't double, but it will feel puffy.)

Brush Danish with beaten egg white. Bake until nicely golden brown, about 16 to 18 minutes. Enjoy warm.