- Grapes were weighed with stems.
- Concord grapes' skins slip off really easily, which is great for the jam portion of this recipe, but a bit tedious for the cake part. Use a sharp paring knife to cut the grapes in half and use its tip to help remove the seeds. If the skins fall off, don't worry—include them in the mixture anyway as they will melt perfectly into the cake during baking.
- Concord grapes are incredibly jam-like and sweet--do not substitute other varieties of grapes in this recipe.
- For the Cake
- 3 tablespoons unsalted butter, melted
- 2 large eggs, at room temperature
- 1/2 cup packed light brown sugar
- 1/2 teaspoon salt
- 1/3 cup sweet white wine, at room temperature
- 1/3 cup milk, at room temperature
- 3/4 cup vegetable oil
- Finely grated zest of 1 lemon
- 1 1/2 cups all-purpose flour
- 1 tablespoon baking powder
- 12 ounces Concord grapes, split in half, seeds removed (See Notes)
- For the Concord Grape Jam
- 1 pound Concord grapes (see notes)
- 1 cup sugar
- 1 tablespoon lemon juice
For the Cake: Adjust oven rack to middle position and preheat oven to 375°F. Grease 9-inch round cake pan with 1 tablespoon butter. Line bottom of pan with parchment paper and coat and grease once again with whatever butter is left on the pastry brush.
Beat eggs and brown sugar on medium-high speed until pale yellow and foamy, about 2 minutes. Add salt, wine, milk, oil, and lemon zest and beat until combined, about 1 minute.
Combine flour and baking powder in small bowl. Lower mixer speed to low and add flour mixture. Beat just until combined, scraping sides and bottom of bowl with rubber spatula as necessary. Fold in grapes.
Scrape batter into prepared pan and bake until cake tester inserted in middle of cake comes out clean, rotating pan halfway through baking, 25 to 30 minutes.
Cool cake in pan about 10 minutes, then turn over onto large plate. Immediately invert onto cooling rack set over parchment-lined baking sheet (to catch any drips).
For the Concord Grape Jam: While cake is cooling, place a small plate in the freezer.
Remove the grape skins by pinching the grapes and place them in a food processor. Pulse with 1/4 cup sugar until completely pureed.
Combine pureed skins, peeled grapes, lemon juice, and remaining 3/4 cup sugar in medium heavy-bottomed saucepan. Bring mixture to boil over medium-high heat, then reduce to medium-low and simmer, stirring frequently, until thickened and reduced to 1 cup, 25 to 30 minutes.
Strain hot jam into a glass measuring cup; discard seeds (strained jam will measure about 3/4 cup). To test for doneness, drop a tablespoon of jam on the chilled plate and allow to stand for 1 minute. Tilt the plate: if the jam runs, return it to the saucepan and simmer 3 to 5 minutes and test again. Jam is done when it stays in a mound.
Spread warm jam over warm cake and let cool completely, about 1 hour. Serve.