This study aimed to investigate the optimum ratio between modified cassava flour, sago flour, and cornstarch in order to improve the physicochemical and sensory qualities of seasoned flour. To achieve this objective, the D-optimal method in Design Expert software was used to create 16 formulas. The respective ranges for modified cassava flour, sago flour, and cornstarch were 37.5%–42.5%, 27.6%–32.5%, and 16.0%–20.0%. Furthermore, moisture content, water holding capacity (WHC), oil holding capacity (OHC), and sensory acceptance were analyzed. With a desirability value of 0.774, the predictive results showed that the optimal composition of 41% modified cassava flour, 31% sago flour, and 16% cornstarch produced the best results. According to physicochemical and functional analysis, the optimum seasoned flour formula had 8.06% moisture content, 6.32% ash, 2.67% protein, 0.40% fat, 80.31% carbohydrate, 5.01% resistant starch, 18.52% WHC, and 10.20% OHC.