Preheat the oven to 350ºF with a rack set in the center position. Line a rimmed baking sheet with parchment paper or a silicone mat.
In a large bowl, stir the oats, sliced almonds, cacao powder, cinnamon, cardamom, and salt until evenly mixed.
In a medium bowl, whisk together maple syrup, oil, almond and vanilla extracts. Pour over the oats and stir to combine. Transfer to the baking sheet and smooth into an even layer.
Bake, rotating the sheet front to back after 20 minutes, until golden-brown throughout and darker on the edges, 35 to 45 minutes. Remove from the oven and cool in the pan. Transfer to a large bowl.
When the granola is completely cool, grate the dark chocolate over the bowl using the large holes of a box grater. Add the cacao nibs and stir until evenly distributed. Add a sprinkle of flaky salt, if you like.
To store: Keep in an airtight container, away from heat and light, for up to 3 weeks.