Wash and rinse the rhubarb stalks and cut them into ½ inch pieces. Be sure to remove all of the leaves before chopping.If using frozen, no need to thaw and you can skip this step.
Place the rhubarb into a baking dish (9x13 inch/23x33 cm). Then add the sugar, flour, lemon juice, lemon zest, and cinnamon. Toss to combine.
Cube the butter - it should still be cold from the fridge.
In a large bowl, combine the butter with the sugar, flour, cinnamon, and salt. I like to use my fingers to combine the ingredients, forming little crumbs. You can also use a fork.Once mixed, add the rolled oats and chopped pecans (if using) and toss to combine.
Sprinkle the streusel topping over the rhubarb mixture.
Bake in the oven to 375°F/190ºC for 35 minutes or so until the rhubarb is tender and the crisp topping is golden brown.Allow cooling for 5-10 minutes before serving. Enjoy with ice cream or cream.
Notes
How to store: Keep any leftovers wrapped or in an airtight container in the fridge for up to 5 days. How to freeze: You can freeze this dessert before or after you bake it. If baked, make sure it's completely cooled before freezing. Cover the baking dish with foil or an airtight seal and put it in the freezer for up to 3 months. To cook from frozen: To bake the frozen raw crisp, allow it to thaw completely. Then bake as per the recipe adding a few extra minutes if necessary. To reheat: To reheat the frozen crisp (that's already baked), first allow it to thaw. Then reheat in the oven at 350ºF/175ºC until the crisp starts bubbling.Check the blog post for more serving recommendations.