For the jam: It is best made the day before it's needed. Puree the banana with the lemon juice in a food processor. Combine 1/2 cup of the puree with the sugar in a small saucepan set over low heat and stir until the sugar is dissolved. Increase the heat, bring to a boil and add the pectin directly to the boiling puree. Bring it back to a boil, remove from the heat and pour into a heatproof bowl. Place the bowl over a bowl of ice to quickly chill the jam, stirring often to cool. Transfer the cool jam to a covered container and refrigerate. The jam can keep for 1 to 2 weeks if kept cold. For the brownie brittle: Preheat the oven to 350 degrees F.
Put the bacon pieces in a food processor and pulse 7 or 8 times, just enough to grind the bacon, not liquefy it.
Set a large saute pan over medium heat until hot, then add the ground bacon. Cook, stirring often, until the tiny pieces of bacon are well cooked and crispy (think bacon bites at a salad bar). Be careful, the tiny pieces tend to pop and become airborne. Remove all the bacon and save all the bacon fat by pouring through a fine strainer, capturing every drop of fat. Set the bacon bits aside. Measure out 4 tablespoons of the bacon fat. Mix in the vanilla extract, set aside and keep warm.
Sift together the flour, milk powder, cocoa powder, instant espresso powder, salt and baking powder and set aside.
Put the egg whites in a medium bowl and whisk for 1 minute until frothy. (Alternatively, use an electric mixer.) Gradually sprinkle in the sugar, whisking until the whites are thick, fluffy and forming ribbons when the whisk is lifted from the bowl. Carefully fold a quarter of the whipped whites unto the dry ingredients. Gently fold that mixture into the remaining egg whites. Fold in the bacon bits, the warm bacon fat, and the toffee pieces.
Spray two perfectly flat sheet pans with nonstick spray. Divide the brittle mixture between the two pans and spread evenly, keeping the brittle very thin. Bake until fully baked (we're aiming for a crisp brittle-like texture), 12 to 14 minutes. Remove the pans from the oven and let cool for at least 30 minutes. Reduce the oven to 275 degrees F.
Break up the brownie brittle into random shapes and sizes, leaving them on the sheet pans. Bake until very crisp, another 5 to 10 minutes. Let cool completely.
To serve, you can make a traditional brownie brittle sandwich filled with Marshmallow Fluff and banana jam: Take a spoonful of banana jam and top it with a spoonful of fluff. Or, place the brownie brittle in a large bowl (think chips and salsa) and fill bowls with Marshmallow Fluff and the banana jam. Have your guests make their own desserts. Great for kids' birthday parties.