Make simple syrup: Combine the granulated sugar and 0.25 cup water in a small saucepan over medium heat, stirring until the sugar dissolves and the syrup is clear, 2–3 minutes. Set aside to cool while you brew.
Put the ice into a heatproof pitcher.
Brew strong coffee using 4 tbsp medium‑ground coffee and 12 ounces just‑off‑boil water (200°F) with a pour‑over, drip machine, or French press. Aim for a total brew time of 3–5 minutes; it’s done when dripping stops or a French press has steeped 4 minutes.
Immediately pour the hot coffee over the ice in the pitcher and stir until chilled and about half the ice has melted, 30–60 seconds.
Divide the iced coffee between two glasses. Sweeten to taste with the simple syrup and add milk if desired. Serve immediately.