For the pear butter glaze: Combine the pear sauce, sugar, bourbon, cardamom and lemon juice in a saucepan and cook, stirring constantly, until it reduces by half, 25 to 30 minutes. Reserve 1/2 cup of the glaze to slather on the chickens as they cook, and the rest for serving.
For the roasted chicken: Preheat the oven to 425 degrees F.
Pat the chickens dry and sprinkle liberally all over with salt and pepper. Divide the rosemary, lemon rinds and fennel between the cavities of both chickens. Tie the legs with butcher's twine and tuck the wings under the chickens.
Place the chickens in a roasting pan and roast for 45 minutes. Remove the pan from the oven and slather the chickens generously with the reserved pear butter glaze. Roast until the juices run clear when pricked, 15 to 20 more minutes. Let rest for 5 minutes to allow for carryover cooking.
For the fennel salad: Meanwhile, toss the shaved fennel with the lemon juice, a drizzle of olive oil and salt and pepper to taste and place on a platter.
Slather the chickens generously with more of the pear butter glaze and put the chickens on top of the shaved fennel salad. Garnish with fennel fronds. Serve with the remaining glaze.