Preheat the oven to 175 C and line a baking tray with a silicone mat or non-stick baking paper.
In a smaller bowl, beat the butter briefly with a whisk or spatula until smooth, then whisk in the yoghurt, honey and vanilla. Add the sugar and whisk well to combine. The mixture might appear slightly curdled, but don't worry.
Add the oats, then sift in the buckwheat flour baking soda, cinnamon and salt, if using. Fold it all together till you have a soft, slightly sticky dough. Some readers have reported finding the dough a little crumbly. If this happens, add a tablespoon of milk to bring it together.
Fold in the chocolate chips. This dough will not spread much so there is no need to chill it.
Use a cookie scoop or a spoon to make 10 to 12 equal portions of the dough and space them apart about 2 inches on the baking tray. Flatten them almost all the way as they won't spread as they bake. Bake for 12 to 15 minutes until the edges are lightly browned. If they still remain puffy, use the back of a spoon to flatten further. While the cookies are hot, press a few more chocolate chips into the top of each one.
Allow the cookies to cool slightly, then place on a wire-rack to cool completely and firm up. They will have crisp edges while freshly baked, but once covered, these cookies will soften partly because oats are highly absorbent and buckwheat doesn't give the same texture as all-purpose flour. Store at room temperature for a week in an airtight box. Happy baking!