Preheat the oven to 160°C (320°F) and line a 12 hole muffin tin with muffin cases.
Melt the coconut oil and chocolate in a glass bowl over a pan of gently simmering water. Set aside to cool.
Place the eggs, coconut sugar, maple syrup, hazelnut butter and vanilla in a medium jug and whisk until smooth. Mix into the cooled chocolate mixture until well combined. Then mix in the buckwheat flour, cocoa powder, bicarbonate of soda and salt.
Divide between muffin cases, press a few chopped hazelnuts into each muffin and sprinkle with flaked salt. Bake for 20-25 minutes or until just set.
Notes
Store in an airtight container in the fridge for up to one week or the freezer for up to one month.