Let the bars cool fully before slicing so they set properly and cut cleanly.

To avoid soggy bars, rhubarb should be thickened well with cornstarch.

Do not overmix the crumble topping. A loose, pebbly mixture gives a crisp texture.

Quick oats can be used, but the topping texture will be less ideal.

Whole wheat flour can replace all-purpose flour for a nuttier taste, though the bars may be denser.

A 1:1 gluten-free flour blend with xanthan gum can be used for a gluten-free version.

Use certified gluten-free oats if needed.

Regular sugar plus 1/2 teaspoon vanilla extract can replace vanilla-infused sugar.

Unsalted butter can be used by adding about 1/4 teaspoon salt per 1/2 cup butter.

Arrowroot powder or tapioca starch can replace cornstarch in equal amounts.

Only rhubarb stalks should be used. The leaves are toxic.

Store in an airtight container at room temperature for up to 2 days or refrigerate up to 5 days.

Place parchment between stacked bars to keep them from sticking.

Freeze individual bars, wrapped and stored in a freezer-safe container, for up to 3 months.

Thaw overnight in the refrigerator, then let sit at room temperature about 30 minutes before serving.

Warm briefly in the microwave for 10 to 15 seconds if desired.

Serve plain or with vanilla ice cream, whipped cream, coffee, or tea.