Ingredients

For Creme Fraiche Ice Cream:
1/2 vanilla bean
2 cups creme fraiche
1 cup half-and-half
2/3 cup sugar
6 egg yolks

For the Rhubarb Crisp:
1/2 cup walnuts
1 cup plus 3 tablespoons all-purpose flour
1/2 cup rolled oats
1/3 cup packed light brown sugar
1/2 teaspoon cinnamon
Pinch salt
1/3 cup unsalted butter, at room temperature
2 pounds rhubarb, washed, trimmed and cut into 1/2-inch slices, about 6 cups
3/4 cup sugar

To make the Creme Fraiche Ice Cream: Split the vanilla bean in half lengthwise and scrape the fine black seeds into a medium saucepan. Add the vanilla bean pod, creme fraiche, half-and-half and sugar, and warm the mixture over medium heat, stirring occasionally, until the sugar has dissolved, 3 to 5 minutes.
In a medium bowl, whisk the egg yolks just until blended, then whisk in about one-quarter of the warm half-and-half mixture. Return the yolk mixture to the saucepan and cook over medium heat, stirring constantly, until the custard coats the spoon, about 10 minutes. Strain the custard into a medium bowl to remove any lumps and let cool to room temperature, then refrigerate until fully chilled. When cold, pour the mixture into an ice-cream maker and freeze according to the manufacturer's instructions. Transfer the ice cream to an airtight container and freeze until set, at least 2 hours.

Directions

To make the Rhubarb Crisp: Preheat the oven to 375 F.

Scatter the walnuts in a baking pan and toast in the oven until lightly browned and aromatic, about 5 minutes, gently shaking the pan once or twice to help the nuts toast evenly. Let cool, then coarsely chop the walnuts. Leave the oven set at 375 F.

For the topping, combine 1 cup of the flour, oats, brown sugar, cinnamon and salt and stir to mix. Working quickly with your hands, mix in the butter until the mixture has a crumbly texture, then stir in the chopped walnuts.

Put the rhubarb in a large bowl and sprinkle the sugar and the remaining 3 tablespoons of flour over. Toss to mix evenly and let stand until the rhubarb starts to release its juices, about 5 minutes. Put the rhubarb in a 12-inch oval baking dish and spread out evenly in the dish. Sprinkle the topping over the fruit and bake until the rhubarb is tender and bubbling and the topping is golden brown, about 45 minutes. Serve warm, with scoops of Creme Fraiche Ice Cream alongside. Makes 6 to 8 servings.