Prep the pan and oven: Heat the oven to 325°F (165°C). Line an 8×8-inch (20×20 cm) pan with parchment, leaving overhang on two sides for easy lifting.
Make the crust: Stir crumbs, sugar, melted butter, and salt until the mixture feels like wet sand. Press firmly and evenly into the pan.
Bake for 8–10 minutes, until set and lightly fragrant. Cool for 5 minutes.
Mix the filling: Beat cream cheese and sugar on medium speed until smooth and fluffy, about 2 minutes. Add sour cream, vanilla, and salt; mix to combine.
Beat in eggs one at a time on low, just until incorporated. Do not overmix.
Fill the pan: Pour the cheesecake batter over the warm crust and smooth the top.
Add the dulce de leche: Warm the dulce de leche in the microwave for 10–15 seconds or until spoonable. Drop small dollops over the batter.
Use a skewer or knife to gently swirl, keeping the swirls shallow.
Bake: Bake for 28–35 minutes, until edges are set and the center has a slight wobble. Avoid browning on top.
Cool and chill: Cool in the pan on a rack for 1 hour. Then refrigerate, uncovered, for at least 3 hours (overnight is best) until fully set.
Slice and serve: Lift out using parchment.
Warm a sharp knife under hot water, wipe dry, and cut into bars. Sprinkle with a pinch of flaky salt if you like.