Put all ingredients except the chestnuts in a blender and process until you get a smooth, thick batter. Add more milk, if needed - you should get a thick, but pourable batter. Add the chestnuts and pulse for a few more seconds - the butter should remain a bit textured or lumpy.
Heat your waffle maker. Once it’s hot, add a ladleful of batter, let it spread out, then put the lid on. Cook the waffle following the machine's instructions - it should take about 3-5 minutes.
When it’s ready transfer it to a plate and keep warm.
Make more waffles using up the batter (depending on your waffle maker the batter is enough for about 4 waffles).
Serve the waffles with maple syrup, custard or honey.