Makes about 1 1/2 cups
Heat the oil in a saucepan. Add the onion and sauté over low heat until translucent. Add the garlic and continue to sauté until the onion is lightly browned.
Sprinkle in the flour and stir until it dissolves. Stir in the ginger.
Combine the miso with 3/4 cup of water in a small bowl and whisk until dissolved, then slowly pour into the saucepan. Simmer over very low heat for 3 to 4 minutes; do not boil.
Add the sesame seeds and the optional cayenne. Adjust consistency with water if too thick, then remove from the heat. Serve at once.