Melt chocolate in a pan on low heat, stirring often so it doesn't burn.
Remove from heat and stir in cocoa powder, stirring thoroughly and quickly. Add kefir and sweetener, and stir or whisk until well combined.
Transfer the chocolate mixture to a parchment paper–lined loaf pan and cool completely to room temperature. Place into the fridge for 90 minutes to solidify.
Using a small melon baller, scoop out the truffle mixture and mold into 1-inch balls. If you don’t have a melon baller, use your hands.
Fill a small bowl with the crushed pistachios. Roll the truffles in the pistachios, pressing the nuts gently into the surface. Using a fine-mesh strainer or sifter, dust the truffles with the matcha powder.