Fill a large bowl with 6 cups/1.4 L cold water and add 1 tablespoon of the lemon juice.
Working with one artichoke at a time, snap off the outer leaves until you reach leaves that are three-quarters yellow and one-quarter green (you’ll take off about three outer layers of leaves). Trim the top, removing the green part and spines. Trim any browned part off the stem, then trim around sides of the stem with a paring knife or vegetable peeler, removing the tough green parts and cre- ating a stubby cone shape at the base of the artichoke. Halve the artichoke lengthwise (or quarter if large), then place it in the lemon water to help keep it from browning.
When ready to cook, drain the artichokes. In a medium skillet over medium- high heat, heat the oil. Add the artichokes and garlic and cook, stirring occasionally, until the artichokes begin to brown, 3 to 5 minutes. Add the stock, thyme, and the remaining 1 tablespoon of lemon juice. Bring to a boil, lower the heat to a simmer, cover, and cook until the artichokes are tender, about 5 minutes.
Use a slotted spoon to transfer the artichokes to a medium bowl. Set aside. Increase the heat under the skillet to high and cook the liquid until it’s reduced by half, 2 to 3 minutes. Remove from the heat and add the butter (if using), stirring until it melts. Return the arti- chokes to the pan and toss with the sauce. Add salt and pepper to taste.