Combine the flour, melted butter, sugar, yeast, milk and egg in a large bowl. Knead until you have a smooth, elastic dough. Set aside and let rise for 45 minutes.
To make the filling heat the treacle, brown sugar, butter and cinnamon in a saucepan over medium heat. Mix well and set aside.
Preheat a pizzelle or shallow waffle iron (see footnote). Knead the dough briefly and divide it into balls the size of a tennis ball (about 4cm in diameter; adjust depending on the size of your waffle iron). Place the ball in the waffle iron and close the lid to cook the waffles until no more steam escapes and the waffle is golden brown.
Remove the waffle carefully with a spatula or palette knife. Use a round cutter to cut off the edges and make a perfect circle. Carefully split the waffle into two rounds whilst still hot. Do not wait too long as they will break if cool.
Spread a little of the filling on one of the halves and then sandwich with the other half. Repeat with the remaining waffles.
Making stroopwafels does require a special shallow waffle iron, as regular waffle irons will produce waffles too thick for this purpose. Try finding a stroopwafel iron, if possible, or improvise with either a pizzelle iron or waffle ice cream cone iron.
For the dried active yeast, 4 1/2 teaspoons is equal to two (7g) sachets.
I wasn't certain if I should use golden syrup or black treacle for this recipe, but judging by the video I decided to black -- something very hard to come by in the US. Also didn't know if I should get light or dark brown sugar, so I used dark. The waffles themselves tasted great, and I was told by friends to not change a thing about them. The syrup on the other hand was very, very rich, and because of the treacle had a very, condensed raisin-like taste. After cooking them, they were almost unbearable to eat because of the richness. They did however became better as they sat on my kitchen counter covered by cellophane in the days that followed. I became slightly addicted to them, and so did my neighbor. I'm not sure my other friends and family would appreciate them as much as we did. That being said, I'd like to try the recipe with light brown sugar, or maybe even white sugar to cut that dark treacle flavor. I also might sub the treacle for Lyle's Golden Syrup and add a little vanilla extract. The syrup too seemed impossible to store, as it solidified after it cooled, and was a nightmare to clean off my utensils and out of my bowls and pans. This is my first time cooking any kind of caramel, though! - 17 Sep 2013