Position an oven rack in the top third of the oven and preheat to 350 degrees F.
Put the bacon slices on a rack set over a baking sheet. Bake until golden brown and crispy, 20 to 25 minutes. Allow to cool slightly, and then crumble or cut with a knife into bite-size pieces. Remove the rack from the baking sheet and reserve the baking sheet with the bacon fat. Increase the oven temperature to 400 degrees F.
Quarter each date lengthwise. Cut each quartered piece into 4 pieces, yielding 32 pieces total.
Put the panko breadcrumbs and milk into a large mixing bowl and let the mixture sit for 2 to 3 minutes so that the breadcrumbs can absorb the milk. Add the ground beef, crumbled bacon, half of the chopped parsley, the egg, 1 teaspoon kosher salt and some black pepper and use your hands to mix until just combined.
Place 1 tablespoon of the meat mixture in the palm of your hand. Flatten it slightly and place 1/2 teaspoon crumbled blue cheese and 1 to 2 pieces of the dates in the center. Top with 1 more tablespoon of the meat mixture and enclose the filling, rolling the mixture in the palms of your hands to form a round meatball. Place the meatball onto the baking sheet that was used to cook the bacon. Roll the meatball around in the rendered bacon fat to evenly coat. Repeat this process with the remaining meat mixture and filling, making about 24 meatballs total.
Bake the meatballs until browned and cooked through, 15 to 18 minutes. Garnish with the remaining chopped parsley and place a decorative toothpick into each meatball.