If you don't have a microwave, preheat oven to 180°C.
In a small bowl, whisk together buckwheat flour, baking powder, salt and nuts.
Add vanilla, maple, butter/oil and milk and whisk to gently combine. Do not overmix.
Transfer to a mug (or ramekin, if baking) and microwave for 70-90 seconds or bake for 18-22 minutes (depending on size of ramekin) until puffy on top but slightly gooey.
Once cooked, top with yoghurt and serve immediately.