Not Manstein's plan
From the post author Nekronion: The plan I imagine is something like this
1. Take the small strip of land that connects Leningrad to the rest of the Soviet Union
2. Evade Leningrad at first and move East and secure the shore of the Lake Lagoda, to cut the city of of any supplies or reinforcements.
3. Link up with the finns in the north and then have Leningrad encircled from all sides.
Points 1&2 Nekronion rightly has AGNorth ignore assaulting the city and instead launch an attack upon the approaches / supply lines to the city. The goal= to fully isolate Leningrad from the Soviets to the south and west. In any case, 18th Army OTL 1943 would need serious additions for any Spring / Summer ofensive
Point 3... Nekronion is incorrect if he believes the Finns had ANY willingness to advance from their winter 1941 Karelian defensive line. Indeed, February 3 '43, as the last German units surrender at Stalingrad... Mannerheim and the Fin leadership decide war is lost and to have Treaty of Moscow version 2.0 ASAP.
So with apologies to Nekronion.... KG offers the following timeline & POD.
OTL 1942 Russian offensive operations
Lyuban / Volkhov Operation (January 1942 - April 1942)= OTL Failure
Sinyavin Offensive (Aug '42 - Sept '42)= OTL Failure
OTL 1943 Russian offensive operations
Operation Iskra / Spark January 12–22, 1943 = OTL Germans forced back from Lake Ladoga.
OTL Operation Polyarnaya Zvezda / Polar Star will start Feb 10 1943
The POD that cancels the Death ride of Citadel / Kursk and greenlights a encirclement of Leningrad?? No Hitler is not killed in EITHER of the barely failed bomb attempts of March 1943. [Although that certainly would have prevented the OTL Battle of Kursk.]
1st POD: Nov 1942 Despite pressures in the south, Hitler retains some of the Operation Northern Light / Nordlicht forces [a couple extra IDs from 11th army & BIG seige guns and other anti-seige elements] in Army Group North. The heavy siege artillery that shattered Sevastopol target the Oranienbaum pocket in preparation for BETTELSTAB ("beggar's staff"). Hilter may be in trouble in STALINgrad, but he wants the biggest Krupp guns to pound the outskirts of LENINgrad.
Jan 18 43 Operation Iskra / Spark: Soviet forces link up at Workers’ Housing Estate #5. A 5 by 6 mile Land corridor of peat bogs is opened to the city. Within month, a land RR connection supplies the city for first time since late 1941.
Jan 25 1943 Soviet success of Iskra on the shore of Ladoga causes a “spark” in Hitler. As he learns that von Paulus’ last runway was lost, Hitler knows the Battle for STALINgrad is over. Manstein’s battered panzers could not relieve the seige. Hitler vows to turn the tables on Stalin and turn LENINgrad into a mirror of Stalingrad. Hilter listens as Kuechler of AGN, Zeitzler and Kluge all argue [true to OTL] that Iskra would have failed if any infantry reserves existed for AGN. Their combined voices connect with Hitler’s “spark.”
They are shocked when Hitler declares more reserves for counter attacks are needed. The Soviet Op MARS hit Rzhev and Hitler allows the immediate withdrawal from the exposed Rzhev salient [OTL Von Kluge allowed to withdrawal March 1943]. They also ask if Hitler approves the withdrawal from Demyansk salient [OTL Hitler approved Jan 31 after a week of debate.]
“No.”
Hitler knows he needs a victory to reprove German power. He needs the Finns to remain in the fight. He orders old operational plans from 1942 brought for his review: BETTELSTAB: for the Oranienbaum pocket; MOORBRAND: for the area near Kirishi... and more importantly he wants the newest maps of the bridgeheads over the Volkhov River, the area of Staraya Russa, and terrain between Lake Ilmen and Valdai Hills just north of the finger thin Demyansk salient…