Start the dough 48 hours before you want to eat them. Mix together the starter and flour. Once it's shaggy looking, get your hands in there and knead it for 5-10 minutes until it's smooth. Cover and refrigerate for 24 hours.
At 24 hours, bring to room temperature. Drizzle with the olive oil and sprinkle on salt. Knead to incorporate for 2-5 minutes. Return to the bowl. Cover and refrigerate for another 24 hours.
Making the Filling
Bring your cream cheese to room temperature for easier mixing.
Stir in the minced red onion, capers (chopped if you prefer), chopped salmon, and dill.
Refrigerate until you're ready to assemble. This can be done at the 24-hour mark or the morning of. The longer it chills the more the flavors marry.
Assembling Your Sourdough Bagel Bombs
The morning you want to serve them, bring the dough to room temperature. Split it into 8 equal portions (mine weighed 80g each; you should weigh the mass and divide that number by 8 to know what each portion should weigh).
Roll each portion of dough out to about 6-inches in diameter.
Spoon about 2-Tbsp of the filling into the center of each dough round.
Pinch up all 4 corners to the center. Then, pinch up the 4 corners created by the first folding.
Pinch all the seams to seal. Then flip the ball over so the seam-side is on the counter. Roll it with your hand to seal tighter.
Once all 8 balls are sealed up tightly, let them rest for 30 minutes on floured surface, covered.
While your balls rest, start a large pot of water to boil. Add baking soda to the boiling water. Also, preheat the oven to 400ºF.
Boil each dough ball for 5 seconds until dough looks darker and slightly wrinkly. Gently remove with a slotted spoon and pat dry. Move to a lined baking sheet while you complete the others.
Mix the egg with 3 Tbsp of water and brush onto the tops and sides of all your bagel bombs. Sprinkle thoroughly with Everything Bagel seasoning.
Bake for 20 to 30 minutes until they are a nice golden brown. When you tap the bottom, they should sound hollow-ish, but remember there is cream cheese in the middle.
Allow them to cool before serving. They're best served at room temperature.