Zest the lemon, taking care to remove only the yellow skin and not the bitter white pith. Set the zest aside and keep the lemon in the refrigerator until you are ready to serve.

Gently crush the black peppercorns, cloves, and cardamom pods using a mortar and pestle or spice grinder to crack the husks. Combine the crushed spices and water in a saucepan and bring to a boil over medium-high heat.

Reduce the heat to medium and boil gently for 10 minutes to fully infuse the water with the spices. Remove the pan from the heat and stir in the reserved lemon zest, mint leaves, and loose-leaf tea.

Allow the mixture to steep for 5 to 7 minutes. A longer steep will create a bolder tea flavor with more pronounced tannins.

Strain the tea through a fine-mesh sieve into a heatproof pitcher, discarding the solids. Cover the pitcher and refrigerate until fully chilled, at least 3 hours or up to 2 days.

When ready to serve, juice half of the chilled lemon and thinly slice the other half. Stir the maple syrup and lemon juice into the chilled tea, adjusting both to your preferred balance of sweetness and acidity.

Fill tall glasses with ice and pour the tea over. Garnish with the lemon slices and additional mint leaves, and serve immediately while ice-cold.