The purpose of the liqueur is to intensify the licorice flavor of the fennel. If you don't have anise-flavored liqueur, or are avoiding cooking with alcohol, you can achieve a similar effect by adding a star anise pod to the stock when you are braising. If you aren't a fan of the licorice flavor, then just skip this step.
1 Cut the tops off the fennel bulbs, chop 2 tablespoons of the fronds and set aside. Slice the fennel bulbs in half, lengthwise, through the core. Slice each half lengthwise into quarters (you should get eight pieces total out of each fennel bulb), leaving some of the core attached so the pieces don't fall apart as they cook.
2 Melt the butter in a large saut? pan over medium-high heat and place the fennel pieces in the pan in a single layer. Reduce the heat to medium and cook the fennel pieces, without moving them, for at least 2 minutes. Sprinkle the salt and sugar over the fennel (the sugar will help with caramelization). Check for browning, and cook for another minute or two if they're not browned yet. Turn the fennel pieces over and brown the other side.
3 When both sides of the fennel are nicely browned, add the ouzo to the pan. Increase the heat to medium high. The ouzo should boil down quickly. When it is almost gone, add the stock and water.
4 Bring the liquid to a boil, then reduce the heat down to low, cover the pan and simmer for 15 minutes. Remove the cover, increase the heat to high and let the stock cook down until it is a glaze. Add the fennel fronds and most of the orange zest and combine gently.
5 Serve garnished with the rest of the zest and a few splashes of lemon juice.
Serves 4.