Today I made the first fillets of many to come. I used a mixture of epoxy, wood flour, and I added a bit of colloidal silica in hopes that it would make a little smoother mixture. Not sure if that helped. On past boats I've just used epoxy and wood flour.
Turned out pretty nice, I think. After this has hardened I'll install the fiberglass on the outside corners and this part can be set aside for later installation.