FROSTING: Put a small/medium bowl in the freezer to chill. In a separate large mixing bowl, beat cream cheese and butter until smooth. Beat in sugar, then jam. Remove that chilled bowl from the freezer and beat cream in that chilled bowl until peaks form. Fold whipped cream into frosting. Cover; chill for a couple of hours until it's firm enough to spread. (If you are in a hurry, you could put the frosting in the freezer to chill quickly.)
CAKE: Preheat the oven to 325 degrees F. Butter and flour two 9-inch cake pans with 2-inch high sides. (I used 10" cheesecake pans - aka springform pans - because they were the only round pans I had with high enough sides and they worked great!) In a medium bowl, whisk together flour, salt, baking powder, and baking soda. In a large bowl, cream butter and sugar together until light and fluffy. Add eggs, one at a time, beating after each addition. Beat in vanilla. Add sour cream, and beat for 30 seconds. Add flour mixture in three additions, beating to blend after each addition. Divide batter into prepared pans.
Bake cake until a toothpick inserted into the center comes out clean, 50-60 minutes. Remove from oven and cool for 10 minutes. Run a sharp knife around the edges of the pans, then turn cakes out onto a rack to cool completely. I threw the two cake layers in the freezer for about an hour to make the cake assembly easier.
Using a serrated knife, divide each layer in half horizontally. Place one half, cake side down, on a cake plate.
Spread 3 TBSP of strawberry jam over the cake, then spread 3/4 c of the frosting over the jam. Arrange 3/4 c of the sliced strawberries on top of the frosting in a single layer. Repeat two more times with cake layer, jam, frosting, and strawberries.
Top with remaining cake layer, cut side down. Spread two cups of frosting over the top and sides of the cake in a thin layer, then frost with remaining frosting. Stir remaining jam to loosen, then spoon teaspoonfuls onto the top and sides of the cake. Use the back of a spoon to swirl jam decoratively into the frosting. This recipe makes a very big 4-layer cake that will feed a lot of people. It says it has 12 servings but I definitely think it feeds even more!