In large bowl, whisk sugar with oil; whisk in eggs, 1 at a time, beating well after each addition. Stir in bananas and vanilla. In bowl, whisk together flour, baking powder, baking soda and salt; stir into banana mixture alternately with buttermilk, making 3 additions of flour mixture and 2 of buttermilk. Scrape into greased 8 x 4 inch (1.5 L ) loaf pan. Bake in center of 350 F (180 C) oven until golden, about 1 hour. Let cool in pan on rack for 15 minutes. Remove from pan; let cool completely on rack.
Make-ahead: Wrap in plastic wrap and store in airtight container for up to 2 days or freeze for up to 2 weeks.
Cut banana bread into 3/4 inch (2 cm) cubes and place in large bowl; sprinkle with two-thirds of the chocolate chips. In large bowl, whisk together eggs, milk, all but 1 tbsp (15 mL) of the sugar, the cream and vanilla; pour over bread mixture and toss gently to combine. Let stand for 15 minutes, tossing gently twice. Pour into great a 12 – cup ( 3 L ) oval baking dish. (Make ahead: Cover and refrigerate for up to 1 day). Sprinkle with remaining chocolate chips and sugar. Bake in center of oven 375 F (190 C) until puffed, golden and knife inserted in center comes out clean, about 45 minutes. Let cool on rack for 15 minutes.