Preheat oven to 350 degrees F. Butter 8, 3-inch cake rings and place on a sheet tray lined with parchment paper.
Sift cake flour, baking soda, and salt in a large bowl. Set aside.
Place butter, 1 cup sugar, and lemon zest in the bowl of a stand mixer fitted with a paddle attachment. Mix on high speed until light and fluffy, 5 to 6 minutes. Reduce speed to low and add the yolks one by one, mixing after each yolk. Add vanilla paste.
In a small bowl, combine buttermilk and vinegar. Alternate adding the dry ingredients with the buttermilk and vinegar to the creamed sugar three times, starting and ending with flour. Using a rubber spatula, scrape the cake batter into a large bowl. Thoroughly wash and dry the mixing bowl.
With the clean bowl back in the stand mixer, with a whip attachment, whip the egg whites on medium speed. When they become foamy slowly add the 2 tablespoons sugar. Increase the speed to high and whip the whites until they hold soft peaks.
Fold one-quarter of the whites into the cake mix. Add the rest of the whites, continuing to fold being careful not to over mix and lose volume.
Divide the batter evenly into the ring molds. Place in the oven and bake for 24 to 26 minutes. To check for doneness, insert toothpick into the center of the cakes, and if it comes out dry, they are ready!
Place the cakes in their molds on a rack and allow to cool on the counter for 15 to 20 minutes. Remove the rings and allow to cool completely.
Place the cream, sour cream, powdered sugar, and vanilla paste in a bowl of a stand mixer with a whip attachment. Whip until the cream until soft peaks, 3 to 4 minutes.
To assemble the shortcakes, slice the cakes in half with a sharp serrated knife. Spoon the Peach-Raspberry Jam on the bottom half of the cake. Place the sliced peaches and whole raspberries on top of the jam. Spoon a massive amount of whipped cream on top of the fruit. Top with the second cake layer. Dust with powdered sugar and serve immediately!
Mash the peaches with a potato masher, and place them in a stainless steel saucepan. Mash the raspberries and add to the saucepan with the granulated sugar, lemon juice, and zest. Bring the fruit to a full boil. Boil for 10 to 12 minutes. Stir in the pectin and boil for an additional minute. Remove from heat and pour into a bowl. Place the bowl over a larger bowl filled with ice. To cool, stir the jam every few minutes until it's very cool and thick. Store in the refrigerator for up to 2 weeks in an odor-free airtight container. Makes 3 cups.