I got this recipe from Eating Well magazine. It's a bit healthier than most banoffee pie recipes. My version was gluten-free too (but you don't have to make it gluten-free). It's not too hard to make, just be sure to make the toffee in advance because it requires about 2 hours in the oven.
2 cans (14 oz) sweetened condensed milk
pinch sea salt
1 cup graham cracker crumbs*
3 tablespoons butter, melted
3 bananas, sliced
1 1/2 cups cream
1 tablespoon powdered sugar
1/2 teaspoon vanilla
* I used gluten-free graham crackers, but if you don't have an allergy to gluten or wheat, you can just use normal graham crackers (it should take about 7 whole graham crackers to make a cup of graham cracker crumbs). I place graham crackers in a large ziplock bag and press a rolling pin over the bag to crush the crackers.
To make the toffee, pour the sweetened condensed milk into a glass pie dish or other shallow baking dish. Stir in a pinch of sea salt and cover the dish tightly with aluminum foil. Place the dish into a roasting pan. Place the pan in the oven at 425 degrees. Add hot water to the roasting pan to about 1/2 way up the side of the pie dish. Bake for about 2 hours or until lightly browned, adding more hot water to the roasting pan as needed. When the toffee is browned, remove from oven and stir until smooth. You can store the toffee covered in the refrigerator for 3 to 5 days.
To make the crust, combine the graham crackers and melted butter in a medium bowl. Press the mixture into a 9-inch tart pan or pie pan. Bake the crust at 350 degrees for 10 minutes or until lightly browned. Remove from oven and allow to cool.
To make the whipped cream, use an electric mixer on high speed to whip the cream and powdered sugar in a large bowl. Continue whipping until the cream forms stiff peaks.
To assemble the whole thing... spread about 2/3 of the toffee on the crust. Arrange the sliced bananas on top of the toffee. Top with the whipped cream.
Place about 1/2 cup of the toffee into a small bowl and heat in the microwave for about 20 seconds or until thinned. Drizzle the toffee on top of the whipped cream.