Preheat the oven to 350°F. Lay a piece of parchment paper on a baking sheet. Spread pistachios, hazelnuts and walnuts across paper and bake for 8 to 10 minutes. Keep an eye on them though, because you do not want them to burn. It’s a good idea to stir them around a couple times during the baking time. Once they’re done, remove from oven and pour nuts into a bowl. Put the bowl in the refrigerator to cool.
On the stovetop, place a non-stick sauté pan over medium-high heat. Add the sesame, coriander, and cumin seeds to the pan to toast them. Stir frequently to toast the seeds evenly on each side. After just 2 to 3 minutes you should be able to smell their pleasant nutty aroma. Remove them from heat and pour into a bowl. Place the bowl in the refrigerator to cool.
After the nuts have cooled to room temperature, use a spice grinder to turn them into not quite a powder. I use a coffee grinder as a spice grinder, and it works great! You may have to grind the nuts in a couple batches depending on the grinder’s size. Repeat this process with the toasted seeds and then with the untoasted flaxseeds.
Once all the nuts and seeds are ground, combine them and mix well. Store the spice mix in the freezer to preserve the most flavor and nutrients. If you are going to use the spice quickly, storing it the refrigerator will work, too.