Slice the lemons. Using a mandoline or a sharp knife, slice the lemons into 1/8-inch-thick rounds. Remove any seeds as you go.
3 large lemons
Make the syrup. In a large saucepan, combine the sugar, water and lemon juice and bring to a boil. Reduce the heat to a gentle simmer, then add the lemon slices in a single layer.
1 cup granulated sugar, 1 cup water, 2 tbsp fresh lemon juice
Candy the lemons. Simmer uncovered for 15 to 20 minutes, flipping the slices once or twice as they cook. At 15 minutes, the slices should be tender and translucent with a bright yellow color. For a deeper golden-yellow color, continue simmering for up to 5 additional minutes. Watch them closely toward the end, as cooking much beyond 20 minutes can cause the slices to brown.
Cool. Using tongs or a slotted spoon, transfer the lemon slices to a wire rack or wax paper. Let cool completely before using or storing.