Trim 1 pound raw rhubarb and cut crosswise into ½-inch pieces (about 3 cups). Place in a medium saucepan.
Add ½ cup granulated sugar. If using 1 vanilla bean, cut in half lengthwise, then scrape the back of a paring knife along the cut side of each half to scrape out the seeds; add the seeds and scraped bean pod to the saucepan. If using vanilla bean paste or vanilla extract, add 1 teaspoon. Add ¼ teaspoon kosher salt.
Bring to a simmer over medium heat, stirring occasionally until the sugar is dissolved, 2 to 3 minutes.
Reduce the heat to medium low and simmer gently, stirring occasionally, until the rhubarb is tender and beginning to fall apart, and a sauce is formed, about 8 minutes.
Remove the saucepan from the heat and let cool for at least 10 minutes. Remove and discard the vanilla bean pod. Serve warm, at room temperature, or cold.
