Combine milk and yeast in a bowl. Let stand for a moment to allow the yeast to dissolve. In another bowl, combine flour, butter, sugar, egg, and salt. Pour in the yeast mixture and knead until smooth. Cover the bowl and let the dough rise for one hour. When the dough is almost ready, make the stroop filling. Combine all the ingredients in a saucepan and stir until the butter is melted and the sugar is dissolved. Let it simmer for a while. The stroop will continue to thicken as it cools. Shape the dough into balls weighing about 35 grams each. Make a total of 14. Turn your stroopwafel iron on the highest setting. Place a ball of dough in the iron and close the iron. Don’t flatten the waffle too much; you should still be able to cut through it. Bake for 1-2 minutes until the waffle is nicely golden brown. When the waffle is done, work quickly. Remove the waffle from the iron and immediately use a round cutter to cut out a nice circle of about 8 to 9 cm (3 to 3.5 inches). Place the hot waffle on a cutting board and cut horizontally with a sharp knife. The stroopwafel is very hot, so use an oven mitt to hold it in place. Take half a waffle and spread the (hot!) stroop on it. Place the other half on top, pressing gently if necessary, and place the waffle on a wire rack to cool. Repeat for all the balls.