1. Brown rice or quinoa. 2. Cook couscous in a large saucepan of boiling salted water, stirring occasionally. 3. Spread out on a rimmed baking sheet and let cool. 4. Meanwhile, whisk tomato paste, red wine vinegar, confectioners' sugar, coriander seed, katsuobushi, and 1/4 of the of shiitake mushrooms in a small bowl; set sauce aside. 5. Whisk eggs, milk, cornstarch, olive oil, and 11/2 tsp black pepper in a medium bowl. 6. Fold in couscous and 1/4 of the of shiitake mushrooms. 7. Working in 1/2 of the butter in a large nonstick skillet or well-seasoned cast-iron pan over medium-high heat. 8. Add heaping spoonfuls of couscous batter to skillet, press to 1/4 inches thickness, and cook. 9. Sprinkle pancakes with more shiitake mushrooms and serve with reserved sauce. 10. Couscous can be cooked 2 days ahead; cover and chill. 11. Couscous batter can be made 6 hours ahead; cover and chill.