Bring cranberries, sugar, ginger, and 1 cup water to a boil in a small saucepan. Cook over medium-high heat, stirring occasionally, until cranberries burst and mixture has thickened slightly, about 8 minutes. Let cool completely, then strain through a fine-mesh sieve, gently pressing on solids (pressing too hard will make mixture cloudy).
For each drink, fill a pint glass with ice.
Add 30 ml cranberry syrup.
Top with pilsner (you’ll need about half a bottle per drink)
Stir and serve