Using electric mixer, beat first 6 ingredients in medium bowl to blend.
Add flour; beat until moist clumps form. Gather dough into ball; flatten into disk. Wrap in plastic; chill 30 minutes.
Preheat oven to 350°F. Divide dough into 6 equal pieces. Press 1 piece evenly onto bottom and up sides of each of six 4 1/2-inch-diameter tartlet pans with removable bottoms.
Bake crusts until deep golden brown and cooked through, about 25 minutes. Cool crusts completely in pans on rack. (Can be prepared 1 day ahead. Cover and store at room temperature.)
Melt 2 tablespoons butter in large nonstick skillet over medium-high heat until beginning to brown.
Add half of bananas to skillet in single layer; cook until bananas brown on bottom, about 45 seconds. Using thin spatula, turn slices over; sprinkle 1/4 cup sugar evenly over bananas. Cook until sugar dissolves and turns golden, occasionally swirling pan, about 3 minutes. Turn banana slices over; add 3 tablespoons warm water and continue cooking until caramel thickens slightly, swirling pan, about 2 minutes. Arrange banana slices in each of 3 tartlet crusts; spoon any caramel from skillet over. Clean skillet, then repeat procedure with remaining butter, bananas, sugar, and water. (Can be prepared 2 hours ahead.
Let stand uncovered at room temperature. Warm in 350°F oven 10 minutes before continuing recipe.)
Top each tartlet with scoop of vanilla ice cream.
Drizzle each tartlet with Bittersweet Chocolate-Port Sauce and serve.