Preheat a waffle iron according to the manufacturer's instructions. Sift the flour, baking powder, and salt into a medium bowl and set aside. In a second bowl, use a whisk to beat together the egg yolks and sugar until sugar has dissolved and eggs have turned a pale yellow. Add the milk, melted butter, and vanilla extract and whisk to combine. Add the flour mixture to the egg-milk mixture and whisk just until blended. Do not overmix.
In a third bowl, beat the egg whites with an electric mixer until soft peaks form, about 1 minute. Using a rubber spatula, gently fold the egg whites into the waffle batter. Don't overmix! Coat the waffle iron with nonstick cooking spray, if required, and pour enough batter in the iron to just cover waffle grid.
Close and cook as per manufacturer's instructions until golden brown, about 2 to 3 minutes. In checking for doneness, open the waffle iron carefully and watch out for steam. Do not open the waffle iron, though, for at least 1 minute. Repeat cooking with remaining batter. When each waffle is done, remove using either tongs or a fork.
Preheat the oven to 400 degrees F.
Spread the pecans on a baking sheet and lightly toast in the oven for 5 to 7 minutes. Remove from the oven and let cool, then coarsely chop.
Combine the butter, pecans, shallots and salt in a medium bowl and mix well with a rubber spatula. Spoon the butter mixture into the center of a sheet of plastic wrap or waxed paper, forming a log about 1-inch in diameter. Fold the wrap over the butter and gently push in and under to form a smooth cylinder. Twist the ends to seal. Refrigerate until firm, about 1 hour. (Refrigerate for up to 1 week or freeze for up to 1 month.)
Slice and serve on top of the waffles with the candied bacon.
Preheat the oven to 350 degrees F. Line a broiler pan with aluminum foil, and position broiler rack on top of pan. Lightly coat the rack with the vegetable oil.
Combine the brown sugar and black pepper in a shallow dish, stirring to mix well. Press 1 side of each slice of bacon firmly into the spiced sugar to coat well. Arrange the slices of bacon on top of the broiler rack in a single layer, sugared side up. If there is any sugar remaining in the dish, sprinkle it evenly on top of the bacon slices. Bake until the bacon is crisp and the sugar is bubbly, 15 to 20 minutes. Transfer to paper towels to drain briefly, then to a plate or serving dish to cool. (Can be made several hours ahead) Serve warm or at room temperature.