Put the flaxseed into a skillet and roast for a few minutes on low heat, stirring every few seconds.
When seeds start to pop in larger quantity, put on a lid and take the skillet off the heat.
Let the seeds cool to room temperature.
Transfer seeds to a spice grinder and mix with the salt.
Pulse for a few seconds. If needed repeat until seeds are finely ground.
Notes
To get the maximum benefits of the Omega 3 fatty acids, keep inside an airtight container in the fridge and use within 3-4 days. Never buy flaxseed already ground, because Omega 3 fats oxidize and get rancid very quickly.