Step 1 Bring a small pot of water to boil over high heat.
Step 2 Pour the sweetened condensed milk into an 8- to 10-ounce glass.
Step 3Unscrew the top of the coffee filter. Place the coffee in the filter, then replace the top, screwing it tightly to compact the grounds. Fit the filter over the glass and pour in just enough hot water to wet the coffee. Allow it to hydrate for 30 seconds.
Step 4Loosen the filter screen screw at least 2 full rotations so the water can pass through the coffee. Pour hot water to the top of the filter, replace the filter lid and wait for the coffee to pass through; this should take about 5 minutes.
Step 5Remove the filter and stir the coffee and condensed milk. Fill the glass with ice and serve immediately.