Line a 9x9-inch baking pan with parchment paper so you can lift the bars out easily later. Mix together the graham cracker crumbs, 1/3 cup sugar, melted butter, and salt in a bowl until it looks like wet sand. Press this mixture firmly into the bottom of your prepared pan—I use the bottom of a measuring cup to flatten it evenly. Pop it in the freezer while you make the filling.

In a large bowl, whisk together the cold water, fresh lemon juice, 3/4 cup sugar, lemon zest, and citric acid. Stir well until the sugar dissolves completely—this takes about 2 minutes of steady whisking. Taste it and adjust the sweetness if needed (sometimes store-bought lemon juice needs extra sugar). Set this mixture aside for now.

Pour the heavy cream into a separate bowl and whip it with an electric mixer until stiff peaks form—you'll see the cream go from liquid to fluffy clouds. This should take about 3 to 4 minutes on medium-high speed. Don't over-whip or you'll end up with butter (yes, I learned this the hard way once).

Gently fold the whipped cream into the lemon mixture using a spatula—fold, don't stir, to keep it light and airy. You want to see white streaks of cream mixed throughout, creating that pillowy texture. Fold until just combined, which takes about 20 to 30 gentle strokes with your spatula.

Pour the lemon filling over your chilled crust and smooth the top with a spatula. You want an even layer so every bar gets the same amount of filling when you cut them later. Freeze for at least 4 hours until the mixture is completely solid (I usually leave mine overnight because life happens).

When you're ready to serve, run a warm knife around the edges of the pan and lift out the parchment paper. Cut the bars into 12 pieces using a hot knife—dip it in warm water between cuts so you don't get ragged edges. The knife stays cleaner and the cuts look prettier this way.

Serve your easy frozen lemonade bars straight from the freezer (they melt fast at room temperature). Garnish with fresh mint if you've got it. Store extras in an airtight container in the freezer for up to 2 weeks, though they never last that long around my house.