- 2 egg yolks
- 1 large egg
- 1 cup granulated sugar
- 1/2 cup full-fat sour cream
- 1 tsp baking soda slaked in the vinegar (Note 1)
- 1 Tbsp vinegar
- 1/2 cup butter room temperature
- 1 cup butter-flavor shortening or 1 cup unsalted butter, room temperature (Note 2)
- 4 cups all-purpose flour 1 cup = 150 g (Note 3); mix in 3 cups, then work in the last cup by hand
- 1 cup unsalted butter 2 sticks, room temperature
- 8 oz full-fat cream cheese 1 brick, room temperature
- 1/2 cup heavy cream at least 33% fat, cold
- 1 Tbsp vanilla extract
- 2 cups plum butter thick (Note 4)
- 2 cups pitted prunes packed; makes about 2 cups plum butter
- 1/2 cup water do not add more
- 1/2 cup granulated sugar
- 1 lemon, juiced
- 1 tsp vanilla extract
- 1 cup powdered sugar
- 2-3 Tbsp lemon juice or milk (Note 5)
- 2 tsp unsweetened cocoa powder
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Warm the prunes. Microwave them about 2 minutes, until hot and soft.
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Blend until smooth. Food processor with the sugar, water, lemon juice and vanilla. No extra water (Note 4).
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Cool completely before piping. (See post above for the photo tutorial.)
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Slake the baking soda. Stir it into the vinegar in a small cup and let the foam settle (Note 1).
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Cream the fats. Beat the butter, shortening and sugar for about 1 minute. Add the sour cream, yolks, egg and soda mixture, and mix until combined (Note 2).
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Add the flour. Mix in most of it, then work in the rest by hand until the dough is soft, smooth and no longer sticky (Note 3).
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Divide and chill. Four equal flat disks, at least 30 minutes in the fridge. Heat the oven to 350°F (175°C) with a rack in the middle.
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Roll between parchment. One disk between two sheets, into a rectangle about 9x10 inches and 3/16 inch thick.
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Cut 2-inch rounds about 1/8 inch apart (about 18 per disk), lift away the scraps and slide the whole parchment onto a 12x18-inch rimmed baking sheet. Do not move the rounds one by one. Chill and re-roll the scraps for about 7 more rounds per disk.
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Cut holes in half the rounds with a bottle cap or piping tip, keeping tops and bases even.
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Bake at 350°F (175°C) for about 7 minutes, until the edges are golden. They burn fast. Peel off the parchment, cool, and reuse the parchment for the next disk. (See post above for the photo tutorial.)
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Whip the butter and vanilla for about 5 minutes, until nearly white and grown in volume.
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Add the cream cheese in cubes, a couple at a time, mixing as little as possible after each.
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Whip the cream in a separate bowl and fold it in gently. Do not overfold, it separates easily (Note 6).
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Pipe the fillings. Two bags with 1/4-inch round tips: buttercream on the tops with holes, slightly warmed plum butter on the bases (Note 4). Press together.
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Make the glaze. Stir the lemon juice into the powdered sugar until smooth. Stir the cocoa into a couple of spoonfuls and cover with plastic (Note 5).
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Glaze the tops with a teaspoon, or dip them and scrape off the extra.
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Drizzle the cocoa glaze from a zip-top bag with a tiny corner snipped off, in both directions. Let the tops harden.
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Refrigerate at least 24 hours in an airtight container before serving (Note 7).
1. Doubling the batch: changing the servings multiplies every amount straight across, and baking soda should not go up the whole way. Keep the first batch worth in full and add three quarters of it for each extra batch: 1 tsp becomes 1 3/4 tsp when you double, not 2. A full multiple makes the cookies rise and spread more than intended.
2. Shortening or butter: use one or the other. Shortening keeps the rounds crisp at the edges. All butter spreads a little more and browns faster, so watch the first sheet.
3. Measuring flour: 1 cup = 150 g. Fluff the flour, scoop, and level. Weigh it if you can. The dough should be soft and smooth, not stiff. Stop adding flour once it stops sticking.
4. Plum butter: it has to mound on a spoon. If it runs, simmer it in a wide pan until a spoon leaves a line, then cool it. Thick apricot butter works too. No plum butter? Make it from prunes with the optional ingredients above; keep it thick and do not add extra water.
5. Glaze: milk instead of lemon juice gives a softer, whiter glaze. Add the liquid a little at a time until the glaze is smooth and spreadable.
6. Split buttercream: microwave two spoonfuls in 5-second bursts, two or three times, and fold them back in. Repeat until smooth. You are warming it to room temperature, not melting it.
7. The 24-hour rest: about half the buttercream soaks into the cookie overnight and turns it soft. Days two and three are the best.
8. Yield: about 50 sandwich cookies (about 100 rounds) with a 2-inch cutter: each disk rolled to 9x10 inches gives about 18 rounds, plus about 7 more from the re-rolled scraps.
9. Storage: fridge, airtight, up to 5 days. Freeze filled and glazed for up to 2 months, and thaw covered in the fridge.