Slice the jalapeños, removing the seeds if desired for less heat. I like to leave the seeds inside 1 jalapeño and remove them from the rest. If my jalapeños are small, I will use 3. It all just depends on how spicy you want the vodka to be. Add the jalapeños to a large glass jar. Pour over the vodka. Refrigerate for at least 2 hours or up to 1 week. The longer the jalapeños sit in the vodka, the spicier it is going to be, so be tasting it as it sits to check for spiciness. Strain and serve as desired.