Place the 150 g sugar and water in a small heavy-bottomed saucepan, stirring only until every grain is moistened. Cook over medium heat without further stirring, swirling the pan gently if color develops unevenly. When the syrup turns medium amber, about 7 to 10 minutes, remove it from the heat. Slowly whisk in the warm cream, then the butter and salt. The mixture will bubble forcefully. Pour the smooth caramel into a heatproof bowl and cool for about 20 minutes, until lukewarm and slightly thickened.
Heat the oven to 325°F with a rack in the middle, then line a standard 12-cup metal muffin pan with paper liners. Combine the graham crumbs, 25 g sugar, and melted butter until the mixture resembles evenly damp sand and holds together when squeezed. Divide it among the liners, about 1 1/2 tablespoons each, and press firmly into level layers using a flat-bottomed measuring cup. Bake for 5 to 6 minutes, until fragrant and lightly deepened in color, then cool the pan on a wire rack.
Place the softened cream cheese in a large bowl and beat with a hand mixer on low speed for about 45 seconds, scraping the bowl and beaters halfway through, until smooth and free of firm lumps. Add the 100 g sugar and sifted flour, then mix on low for another 30 to 45 seconds. Blend in the sour cream and vanilla just until the mixture is uniform. Keep the speed low and stop once smooth because a fluffy, aerated batter is more likely to puff, crack, and sink.
Add the room-temperature eggs one at a time, mixing on low for 10 to 15 seconds after each and scraping the bowl before adding the next. Stop when the final streaks of egg disappear; the finished batter should look glossy, thick, and pourable rather than whipped. Measure 1/3 cup, about 80 g, of the lukewarm caramel and fold it into the batter with a flexible spatula until evenly colored. Reserve the remaining caramel at room temperature for topping after the cheesecakes have chilled.
Divide the filling evenly among the crust-lined cups, using about 1/4 cup per cavity and leaving a little space at the rim. Tap the pan lightly on the counter two or three times to release large air pockets. Bake at 325°F for 18 to 22 minutes. The outer 1/2 inch should look set and slightly matte, while each center should move as one small, cohesive wobble when the pan is nudged. An instant-read thermometer inserted near the center should register about 155°F.
Turn off the oven, prop the door open slightly, and leave the cheesecakes inside for 10 minutes to reduce abrupt temperature change. Transfer the pan to a wire rack and cool for 45 minutes, until the cups no longer feel warm. Do not remove the cheesecakes while warm because their centers are still fragile. Cover the pan without touching the surfaces and refrigerate for at least 4 hours, preferably overnight, until the centers feel cold and firm but retain a slight creamy resilience when gently pressed.
If the reserved caramel has become too firm to spoon, warm it in 5-second microwave intervals, stirring after each, until fluid but not hot. Remove the chilled cheesecakes from the pan and peel away the liners carefully. Spoon about 2 teaspoons of caramel over each top, letting it spread naturally without flooding the edges. Serve the cheesecakes cold for the cleanest shape, or let them stand at room temperature for 10 to 15 minutes for a softer, creamier texture.
