For the bacon jam: In a skillet, saute the bacon over medium-low heat until browned and the fat has rendered, 7 to 10 minutes. Transfer to a paper towel-lined plate. Drain off all but 2 tablespoons bacon fat from the pan.
Reduce the heat to low and add the onions, garlic and mustard seeds to the pan. Saute until the onions are translucent, about 15 minutes. Add the maple syrup, balsamic vinegar, red wine, fish sauce, Worcestershire and cayenne; bring to a simmer, scraping any brown bits from the bottom of the pan with a wooden spoon. Return the bacon to the pan, reduce the heat to medium-low, and cook, stirring occasionally, until deeply caramelized and a jam-like consistency is achieved, 30 to 45 minutes. Transfer to a bowl and chill.
For the flaky bacon bruschetta: Preheat the oven to 375 degrees F. Line a half-sheet pan with parchment and set aside.
In a small bowl, whisk together the egg, water and salt to make an egg wash. Set aside.
Roll the Flaky Pastry Dough into a rectangle slightly larger than 4-by-6 inches. With a very sharp knife, trim the rectangle to exactly 4-by-6 inches and then cut the dough into twelve 2-inch squares. (Note: If the dough is getting warm, transfer it to a parchment-lined pan, cover and refrigerate until chilled, 10 to 15 minutes.)
To form a bruschetta, fold a square of dough in half to form a triangle. Cut two slits parallel to the edges, leaving a 1/4-inch border and taking care to not cut all the way through to the tip; the triangle will resemble an arrow. Unfold the triangle; the dough should now resemble a square within a square.
Brush the surface of the dough with egg wash. Take one cut corner of the outside square (rather than one that is attached to the inner square) and fold it over to the edge of the opposite inside square. Fold the other cut corner to the opposite edge of the inner square. Gently press.
Place 1/2 teaspoon bacon jam in the middle of the formed bruschetta, then brush the edges with egg wash. Transfer to the prepared sheet pan. Repeat with the remaining squares; reserve the remaining bacon jam for another use.
Bake until puffed and golden brown, about 25 minutes. Serve warm, garnished with cherry tomatoes.
Add the flour and salt to a large bowl and stir to combine. Add the butter and toss to combine. With your fingers, begin to "smush" the butter into flat pieces. Continue smushing until all the butter is flattened but none of the pieces are larger than a quarter. The flour will look like coarse cornmeal.
Add the water, quickly folding it in with a wooden spoon to distribute the moisture. (Do not stir vigorously--the dough should appear shaggy.) Use your hands to break up any large clumps of moisture. Then use your knuckles or a palm to smear the dough up the sides of the bowl (a technique known as fraisage). This distributes the butter over a larger surface to achieve larger flakes and compact the dough. Once you've gone around the bowl one time, fold the dough over itself a few times to pick up any dry bits from the bottom. Gently press the dough into a disk. (Note: The dough should remain very cool to the touch throughout the process. If it approaches room temperature, refrigerate it for 5 to 10 minutes to chill.)
Transfer the dough to a lightly floured work surface and roll out to a 10-by-12-inch rectangle. Perform a letter fold by folding one of the short ends towards the middle and the other short end over the first, like folding a business letter.
Turn the dough 90 degrees, so the long side faces you, and perform a second letter fold. Turn the dough 90 degrees again; perform a third letter fold.
If the dough still feels cool, it can be used immediately. Otherwise, wrap it in plastic wrap and chill for at least 20 minutes. The dough can be refrigerated for up to 1 week or frozen for up to 1 month.