First, a couple of notes on cooking with lavender:
-The leaves as well as the flower blossoms are edible.
-If you don't grow it yourself, make sure that you only use lavender that has been produced for culinary usage (often found in bulk form at health food stores). If it isn't sold in a food store, don't use it (such as that in craft stores).
-A little goes a long way. Too much and your mouth will taste like it was washed out with soap.
Now for some of the items I have done with it:
Lavender ice cream (Lavender & Honey even better!) is a common use. Infuse the cream with the lavender buds by bringing it to a simmer and then take off the heat and cover, letting sit for about 30 minutes.
Lavender orange sorbet (infuse lavender buds into the orange juice).
I've also used lavender and thyme in an herb past rub for roasted lamb.
"English Garden Madeleines" using dried lavender and rosewater in the madeleine batter.
I did a presentation on culinary uses of lavender a dozen years ago and don't quite recall what else I did with it but should be able to pull out the recipes I mentioned above.
If you'd like the recipes, email me at: darin@chefdarin.com and I'll forward them to you.
Best Answer
Bolted lettuce tastes bitter; I'd suggest putting it in your compost pile if you have one. Of course, if you like bitter greens, you could make a salad of your lettuce (perhaps with a mix of other greens) with some dried fruit, toasted nuts, and a little goat cheese; the flavors might marry well.