Step 1: Create the Luxurious Filling
In a medium bowl using a hand mixer (or a stand mixer with the paddle attachment), beat the softened cream cheese on medium speed until completely smooth and creamy, about 2 minutes. Scrape down the sides. Add the ¼ cup sugar, vanilla extract, and lemon zest. Beat again until fully incorporated, about 1 minute. Add the single egg yolk and beat just until the mixture is smooth and uniform. Avoid overmixing once the yolk is added. Gently fold in the strawberry preserves with a spatula, creating a marbled effect rather than fully mixing it in. You want beautiful ribbons of strawberry throughout the cream cheese. Cover the bowl and refrigerate for at least 30 minutes to firm up slightly for easier spreading.

Step 2: Assemble the Sandwiches with Precision
Lay out 12 slices of bread. Lightly butter one side of each slice—this will be the inside of the sandwich, and the butter helps create a barrier to keep the bread from getting soggy from the filling. On the buttered side of 6 slices, spread a generous, even layer (about 3-4 tablespoons) of the chilled cheesecake mixture, leaving a ½-inch border around the edges. Place the remaining 6 slices of bread on top, buttered-side-down, to form sandwiches. Press down gently around the edges to seal.

Step 3: Create a Secure Seal
This step is critical to prevent filling leakage during frying. Using the tines of a fork, firmly press down and crimp the edges of each sandwich all the way around. This physically seals the two pieces of bread together. Once crimped, place the assembled sandwiches on a parchment-lined tray or plate, cover loosely with plastic wrap, and refrigerate for at least 1 hour, or up to overnight. This chilling solidifies the filling and firms up the bread, making the sandwiches much easier to handle during battering.

Step 4: Prepare the Frying Station and Batter
In a heavy-bottomed, deep pot or Dutch oven (like a 5-quart size), heat 3 inches of oil over medium heat to 350°F (177°C). Use a deep-fry or candy thermometer to monitor the temperature accurately. While the oil heats, whisk together the custard batter. In a large, shallow bowl (a pie dish works perfectly), vigorously whisk the 2 whole eggs and 1 egg white until frothy. Whisk in the milk, heavy cream, the 2 tablespoons of sugar, vanilla, cinnamon, and salt until combined. Gradually whisk in the flour until you have a smooth, lump-free batter with the consistency of heavy cream.

Step 5: Batter and Fry to Golden Perfection
In a separate shallow dish, mix the 1 cup of sugar with 1 tablespoon of cinnamon for the coating. Working with one chilled sandwich at a time, carefully submerge it into the batter. Let it soak for 10-15 seconds per side, ensuring it is fully coated but not dripping excessively. Let any excess batter drip off for a moment. Gently lower the battered sandwich into the preheated 350°F oil. Fry only one or two sandwiches at a time to avoid crowding and a temperature drop. Fry for 2-3 minutes per side, using tongs or a spider skimmer to carefully flip, until the entire sandwich is a deep, uniform golden brown.

Step 6: Drain, Coat, and Rest
Immediately after frying, transfer the sandwich to a wire rack set over a baking sheet (this keeps it crisp). Allow it to drain and cool for exactly 60 seconds—just enough time for the exterior to set slightly but remain warm. Then, gently roll the entire sandwich in the cinnamon-sugar mixture, coating every surface. Return it to the wire rack. Let the sandwich rest for 4-5 minutes before serving. This rest period is crucial: it allows the molten-hot filling to cool to a warm, creamy consistency and prevents burns, while letting the exterior crisp up further.

Step 7: Serve with Flair
Dust the warm sandwiches generously with powdered sugar. Serve immediately, either whole or sliced diagonally to showcase the beautiful layered interior. Provide a side dish of extra strawberry preserves for dipping and a generous scoop of vanilla ice cream or dollop of whipped cream alongside