Preheat the oven to 350°F (175°C).

Combine graham cracker crumbs and 1/4 cup sugar in a bowl. Stir in melted butter until well blended.

Press the mixture into the bottom of a 9-inch springform pan to form a crust.

Bake the crust for 10 minutes, then let it cool slightly.

In a large bowl, beat the cream cheese and 1 1/4 cups sugar until smooth and creamy.

Mix in the flour and vanilla extract until fully combined.

Add the eggs, one at a time, beating well after each addition for a fluffy texture.

Stir in the sour cream and heavy cream.

Pour half of the cream cheese mixture over the crust.

Drizzle half of the chocolate syrup over the top and use a knife to swirl the layers gently.

Pour the remaining cream cheese mixture over the chocolate layer and drizzle the rest of the chocolate syrup on top, swirling gently.

Bake for 50-60 minutes, or until the center is almost set but has a slight jiggle.

Turn off the oven and let the cheesecake cool in the oven with the door ajar for 1 hour.

Remove from the oven and allow it to cool completely on a wire rack.

Chill in the refrigerator for at least 4 hours before serving.