In a bowl, combine 1/4 cup of the warm water with the baking powder. In a food processor, combine the semolina with the flour, yeast, sugar and the remaining 2 3/4 cups of warm water; process for 30 seconds, until smooth. Add the salt and baking powder mixture and process for 30 seconds longer. Pour the batter into a large bowl, cover with a kitchen towel and let rise at room temperature until doubled in bulk, about 1 hour.