Line an 8-inch square pan with parchment paper, leaving overhang on two sides for easy lifting.
Place the chocolate chips, sweetened condensed milk, and cooled chestnut praline coffee concentrate in the slow cooker. Cover and cook on low for 45 to 60 minutes, stirring once or twice, until the chocolate is fully melted and the mixture is smooth.
Turn off the slow cooker. Fold in 1/2 cup of the chopped praline pieces until evenly distributed.
Spoon the fudge into the prepared pan and level the surface. Scatter the remaining 1/4 cup praline pieces over the top and press them in lightly.
Refrigerate for 3 to 4 hours, or until firm. Lift the slab out by the parchment, cut into 36 small squares, and serve chilled.