Grease and line a 9x13 baking pan with parchment paper, leaving a bit of an overhang on both the long sides, then lightly brush the top of the parchment paper with a little bit of oil or fat of your choice (I like to use coconut oil). Also lightly brush a second sheet of parchment paper of approximately the same size as your pan and set aside.
Preheat your oven to 350°F; spread the almonds, peanuts, macadamia nuts and hazelnuts onto a large baking sheet and bake for 7-8 minutes, until lightly toasted and fragrant.
Once toasted, transfer the nuts to a large mixing bowl and add the pumpkin seeds, sunflower seeds, buckwheat groats and sesame seeds. Set aside.
In a medium saucepan set over medium heat, combine the honey, maple syrup and salt and bring to a boil. Continue boiling until the syrup reaches 260°F (hard ball stage) on a candy thermometer. Stir in vanilla extract and immediately pour the hot syrup over the reserved nuts and promptly stir until well distributed and evenly coated.
Quickly transfer the sticky mixture to the prepared pan and spread evenly throughout the pan with a rubber spatula; cover with the greased sheet of parchment paper (greased side down) and, with the help of a flat object such as flat bottomed drinking glass, press the mixture firmly to close in all the holes and compact the nuts really well.
Let the bars cool at room temperature for about 20 minutes (they should still be slighly warm and pliable at this point), then carefully lift them out of the pan by pulling gently on the parchment paper; cut into 20 bars.
Allow to cool completely, then transfer to airtight container. To avoid sticking, either place a piece of parchment paper between bars, or wrap individually in plastic film.
Store at room temperature in a cool dry place for soft, sticky bars. They will keep for up to a few weeks.
If you prefer a brittle, candy-like texture, keep the bars in the refrigerator (where they will keep for longer, too!)