For the rhubarb, look for firm, crisp stalks with a vibrant pink or red color., Fresh berries are best, but frozen works great too; thaw and drain them well before using to avoid a soggy filling., Frozen rhubarb is a fantastic option when fresh isn’t available; it might release more moisture during baking, so you may want to add an extra tablespoon of cornstarch to the filling to help thicken it up., If the dough is becoming too soft while you’re working with it, pop it back into the fridge for a few minutes to firm up., Pre-baking the crust before adding the filling prevents the moisture from the fruit from seeping in and turning your crust into a soggy mess., Taste the filling mixture and adjust the sugar as needed., Ginger, cinnamon, and almond extract are all wonderful additions that complement rhubarb beautifully., Consider adding chopped nuts for extra crunch and flavor; pecans, walnuts, or almonds would all be delicious choices., For a gluten-free option, you can use a gluten-free flour blend in the topping., Add a bit more rolled oats or chopped nuts to the topping for extra crunch; bake the bars for a few extra minutes to ensure the topping is nice and golden brown., The topping should be a beautiful golden brown, and the filling should be bubbly around the edges., Insert a toothpick into the center of the filling; it should come out with just a few moist crumbs attached., For a gluten-free version, use a gluten-free flour blend in the crust and topping., For a vegan version, swap the butter for a plant-based alternative and use a flax egg., The leaves of the rhubarb plant are poisonous and should never be eaten.