Cut off the top of the jalapeños, then cut them into fine slices.
Combine Tequila and sliced jalapeños with seeds in a large jar.
Close the jar with a lid and shake the mixture shortly before letting it sit in a dark and cool place.
Check your infusion regularly. In the beginning, in very short intervals. If you only want very little heat, check after 5-10 minutes. Then hourly or once a day, depending on how long you want to infuse your Tequila.
Once the Tequila reaches the desired degree of heat, use a fine-mesh strainer and a funnel to strain it into the Tequila bottle.
The infusion will be good for about six months.
If you don't need a whole bottle of spicy Tequila and want to scale down, you can easily do that. Just take one medium-sized jalapeño per 250ml of Tequila