How to Make It
Place flour and teaspoon salt in the bowl of a food processor; pulse until combined. Add butter to flour mixture and pulse until combined. Add cream cheese; process until one large ball forms.Divide the dough evenly into 4 disks; wrap each in plastic wrap and refrigerate for at least 2 hours (up to 24 hours).
Preheat oven to 350°.
Stir together ricotta, capers, dill, lemon juice, salt, and pepper in a medium bowl until combined.
Working one disk at a time (keeping the remaining disks in the refrigerator), roll each dough portion into a 9-inch circle on a floured surface. Spread ricotta mixture evenly over each rugelach dough circle.
Using a pizza cutter, slice the disk into 12 even triangular portions. Gently roll each portion, starting from the widest end, towards the narrow end. Transfer rugelach to parchment paper- or silpat-lined baking sheets.
Whisk together poppy seeds, sesame seeds, onion, garlic, and coarse salt in a small bowl. Brush the rugelach with egg; sprinkle evenly with “everything” mixture.
Bake for 23 to 27 minutes, or until golden brown. Let cool on baking sheet for 5 minutes; transfer to wire rack to cool completely.