Make the plum butter

Preheat the oven to 375 degress. Place 3 or 4 small plates and silver or metal spoons in the freezer. In a 4-quart pot, combine the plums, 2 tablespoons water, and the lemon juice. Scrape in the seeds of the split vanilla bean and toss in the pod, too. Bring it to a boil slowly over medium heat, keeping an eye on it to prevent scorching. Reduce the heat to low, cover, and cook, checking and stirring frequently, until the fruit is very soft, about 20 minutes. Remove and discard the vanilla pod.

Meanwhile, make the almond butter

Lay the almonds on a sheet pan, spreading them in a single layer, and roast them in the oven for 10 to 12 minutes, until lightly browned and fragrant. Remove the pan from the oven and let the almonds cool briefly, about 5 minutes.

Transfer the nuts to a food processor and puree until liquidy, about 6 minutes. Scrape down the sides with a spatula and continue pureeing. With the machine running, drizzle in the coconut oil. Drizzle in the maple syrup, which will make the mixture thicken. Add the salt and continue pureeing. Taste and add more salt if necessary. Add more coconut oil by the teaspoon if the texture needs thinning. Transfer the almond butter to a glass storage vessel.

Finish the plum butter

Set a food mill over a large bowl, and puree the plums, along with their juice, in batches. Return the strained puree to a clean large pot. Place it over medium heat, add the sugar, and stir until dissolved. Increase the heat to high, bring the fruit to a boil, then reduce the heat to a very low simmer. Stirring frequently, simmer uncovered for about 1 hour.

To test for doneness, dip a cold spoon from the freezer into the boiling mixture and pour a spoonful onto one of the cold plates. Return the plate to the freezer for a few minutes, then run your finger through the jam. If the little trench stays intact without the jam creeping back together, the plum butter is done. Otherwise, continue to cook, checking every 10 minutes until it passes this test.

Pour the plum butter into glass jars and allow it to cool completely at room temperature, 2 to 3 hours. Cover the jars and refrigerate until ready to use.

Assemble the sandwiches

Lay 8 slices of bread on a large clean surface. Spread about 1 tablespoon of almond butter evenly over each of 4 slices of bread. Spread about 1 tablespoon of plum butter on each of the remaining 4 slices of bread. Sandwich the slices together and serve.

NOTE: Both the plum butter and almond butter can be made ahead and stored—the plum butter in the fridge for up to 2 weeks, the almond butter at room temperature for the same amount of time. The plum butter recipe also doubles well. When scaling, measure the puree after it has been strained, and for each cup of puree, use 1/2 cup sugar.