While the linguine is cooking, prepare the sauce. In a saucepan, whisk the flour and peanut butter together over low heat. Once warm, whisk in the cream, 2 Tbsp. water, 1 Tbsp. soy sauce, and sugar. Very slowly bring the mixture to a slow bubble. Let bubble, while whisking constantly for 2-3 minutes, allowing the sauce to thicken. Then add the red pepper flakes and salt and pepper to taste. Add a few Tbsp. water to sauce, if too thick.