In a stand mixer fitted with the paddle, combine butter and flour and mix until sandy and evenly crumbly. Add powdered sugar, almond flour, poppy seeds, and salt and mix briefly. Add the egg and vanilla and mix just until a cohesive dough forms. Wrap tightly and refrigerate for 2 hours.
Heat the oven to 340°F/170°C.
Roll the dough to about ⅛ inch/3 millimeters thick. Cut into heart shapes and arrange on parchment-lined baking sheets. Bake until lightly golden, 10 to 12 minutes. Let cool completely.
Meanwhile, prepare the marzipan by mixing it with the egg whites in a stand mixer fitted with the paddle, adding the whites gradually, until smooth and uniform. Cover and set aside.
Prepare the filling by mixing 2 tablespoons/25 grams of the sugar with the pectin. In a saucepan, combine the jam, remaining sugar, and water and bring to a full boil. Add the pectin mixture, reduce heat to medium, and whisk constantly for 3 minutes, until slightly thickened. Tint lightly with red food coloring.
Pipe a thin marzipan border around each cookie using a small star tip. Bake again until the marzipan is just lightly golden, 7 to 10 minutes. Cool completely.
Fill the centers with the warm jam mixture and let set before serving.