Ultimate Refreshing Lemonade 
Prep: 30 mins
Resting Time: 3 hrs
Total: 3 hrs 30 mins
Serves: 4 to 8
Ingredients:
18 green cardamom pods (see notes)
3 pounds (1.3 kg) room-temperature lemons (10 to 12 medium lemons)
14 ounces sugar (2 cups; 400 g)
2 teaspoons green cardamom seeds (see notes)
24 ounces cold water (3 cups; 700 ml)
1 teaspoon Diamond Crystal kosher salt, plus more to taste; for table salt, use half as much by volume
Directions:
Use a mortar and pestle or rolling pin to gently crack open cardamom pods to release their flavor and aroma. Seeds should be visible but not popping out. Set aside.
Roll lemons firmly against the counter to soften their rinds. Halve and juice lemons; pour juice into a sealable container and refrigerate. Cut rinds into 1-inch chunks. In a large nonreactive mixing bowl, mix lemon rinds well with sugar and cracked cardamom pods. Cover with plastic wrap or a lid, and let stand at room temperature, stirring once every 45 minutes or so, until sugar has completely dissolved, about 3 hours. (You can let the mixture stand up to 12 hours, if desired.)
While the lemons macerate, use a spice grinder or mortar and pestle to pulverize the cardamom seeds into a fine powder. You should get between 2 and 3 teaspoons of powder. Set aside in an airtight jar until needed (see notes).
Stir the lemon chunks once more, tasting and smelling the mixture to ensure it has a cardamom aroma and flavor.
Add water, 8 ounces (1 cup) of reserved lemon juice, and 1 teaspoon ground cardamom to the macerated lemons (see notes). Stir well, then strain through a nonreactive fine-mesh strainer or piece of cheesecloth into a glass or ceramic container, pressing to express liquid; discard solids.
Stir 1/2 teaspoon ground cardamom and salt into the liquid. At this point, the concentrated cardamom lemonade can be refrigerated in a tightly sealed glass or other nonreactive container for up to 1 week.
To serve, pour lemonade over ice and adjust to taste with additional water or lemon juice, depending on personal preference; bear in mind, though, that the lemonade will be diluted as the ice melts.
Notes:
I prefer a tart lemonade, so this recipe calls for adding 8 ounces (1 cup) of reserved lemon juice to the lemon rind syrup. If you prefer your lemonade sweeter, start with 6 ounces of lemon juice and taste before adding more.
Green cardamom is generally considered sweeter and more versatile, suitable for both savory and sweet dishes, while black cardamom has a smokier, more robust flavor and is typically used in savory dishes. Do not substitute black cardamom in this recipe.
If green cardamom seeds are unavailable, you can substitute with ground cardamom and omit pulverizing in step 3.
Make-Ahead and Storage:
The concentrated lemonade can be refrigerated in an airtight nonreactive container for up to 1 week.
Reserve any extra ground cardamom in an airtight jar at room temperature for up to 2 months.
Recipe courtesy of Serious Eats.com