Step 1Put the beets in a medium pot and add 2 teaspoons salt and enough cold water to cover. Bring to a boil over medium-high heat, then reduce the heat to maintain a steady boil. Cook until the beets are partially tender, 15 to 20 minutes. When you poke them with a fork, you should feel some resistance. Drain and set aside to cool for a few minutes.
Step 2If you don’t want your hands to be magenta for days, put on a pair of rubber gloves. When the beets are cool enough to handle, carefully peel them without removing any flesh. A paring knife works well for this. Using a melon baller or a paring knife, hollow the beets to create a symmetrical cavity — you want to leave about ½ inch of flesh on all sides. Trim a thin slice from the bottom of each beet so it will sit flat on your work surface, but take care not to slice through into the cavity. Save the beet scraps for adding to smoothies or your lunch salad.
Step 3Heat the oven to 350 degrees. While the oven heats, make the stuffing: Stir together the quinoa, leeks, oil, harissa, 2 teaspoons salt and several twists of pepper in a medium bowl.\
Step 4Fill each beet with the stuffing, leaving a little room at the top for the quinoa to swell when it cooks. Tap the beets gently on the counter to settle the stuffing. Arrange them side by side in a wide baking pan that can hold them all in a single layer. It’s important that the beets fit snugly in the pan or they might roll over. If there’s a gap left, squeeze in a whole peeled onion for support. As the beets cook, the onion will soften, drink up the cooking juices and be a delicious bonus.
Step 5Whisk together the lemon juice, silan, 1 ½ cups water, the remaining 1 teaspoon salt and ¼ teaspoon pepper in a small bowl. Reserve ½ cup of the liquid and set aside. Spoon some of the remaining liquid over the stuffing (the quinoa needs moisture to cook properly), and pour the rest around the beets. Cover the pan with a tight-fitting lid or wrap it tightly with aluminum foil.
Step 6Bake for 30 minutes, then remove the pan from the oven, but don’t turn the oven off. Spoon some of the reserved cooking liquid over the stuffing to keep it juicy. Cover the baking dish again and bake until the quinoa is cooked through and looks swollen and the beets are completely soft, an additional 15 to 20 minutes. Serve warm or room temperature, with chilled yogurt, sour cream or tahini sauce.