Combine flour, sugar and salt in a mixing bowl. With your fingertips, work the butter into the flour mixture until it is well-distributed. Add water, a tablespoonful at a time, until you have a dough that will hold together in a ball. (If you have time, cover the pastry and refrigerate it for 30 minutes at this point.)
Turn the ball out onto a lightly floured surface and divide it into 4 parts. Roll each part into an oblong that is an inch or so longer than your bananas, and wide enough to wrap around one. Lay a banana on each oblong, and roll it up in the pastry, sealing the edges and ends by pinching with fingertips.
Deep fry the pastrt-wrapped bananas, or fry them in an inch or so of hot oil in a large, heavy skillet for 3 or 4 minutes on each side. When done, they should be crisp and golden brown outside, and soft and moist inside. Drain on clean, absorbent cloths, and sprinkle with cinnamon before serving.