1. Submerge the beet greens in a large pot of boiling, salted water and cook briefly, uncovered, until the greens are limp. Drain in a colander set under cold running water. When cool enough to handle, take up the greens by handfuls and squeeze gently to press out the excess water. Chop the greens coarsely and set aside on absorbent paper.
2. Melt the bacon fat in a large skillet. Add the beet greens and stir over medium heat for 1 minute.
3. Meanwhile, combine the lemon juice and brown sugar in a small saucepan and heat until the sugar dissolves. Season the beet greens with salt and pepper, then transfer them to a serving bowl. Pour on the lemon juice mixture and toss lightly to combine. Serve immediately.