1. In an airtight container, combine the apricots, sugar, lemon juice and salt. Cover and let the apricot mixture sit out at room temperature overnight.

2. In a medium saucepan set over high heat, cook the apricot mixture until the apricots are translucent and thick like jam, about 15 minutes. Turn off the heat and place ¼ cup of the apricot mixture in a food-processor bowl with the praline paste; purée. Return the apricot-praline purée back to the saucepan with the cooked-down apricots and stir to combine. Transfer the mixture to a medium bowl and set aside to cool.

3. Toast the bread until it is barely golden. Spread one side of each piece of bread with ½ tablespoon of the butter. Turn two of the slices over and add 1 to 2 tablespoons (depending on the size of the bread slices) of the apricot-praline mixture, spreading it into an even layer. Top with another slice of bread, buttered side facing out.

4. In a grill pan set over medium-high heat (or using a panini press), press the sandwich until golden and ridged; use a spatula to lightly press the sandwich, about 1 minute on each side (2 minutes total if using a panini press). Remove, cut in half on a bias and serve warm. Refrigerate the remaining apricot-praline filling for up to one week or freeze for up to three months. (Use the apricot praline in tarts, cake layers or for making more sandwiches.)