In a large bowl, stir together the instant yeast, flour, sugar, salt and anise seeds (if using). Melt the butter in a small saucepan over low heat, then add the milk. Turn off the heat and allow the miIk/butter mixture to cool to hand temperature if it is too warm. Add the egg yolk and vanilla extract and whisk to combine. Drizzle the wet mixture on to the dry ingredients. Mix with your hands until you have a shaggy looking dough.
Turn the dough out onto a lightly floured surface and knead gently until smooth. Form into a ball, place back in the mixing bowl, cover with a clean tea towel and place somewhere away from drafts to proof until doubled. This will take approximately 1.5 hours at room temperature (21C, 70F). Line or grease a 9x9" baking pan and set aside.
In a medium bowl, mix all the streusel ingredients together with your fingers until it resembles course crumbs. Place it in the fridge to chill.
Once the dough has doubled in size, place it on a lightly floured surface and press it down with your hands into a rectangular shape. Dust the top of the dough with flour, then roll it out to the size of your baking pan. Fold the dough into quarters, place it on your baking pan and unfold it, pressing the dough to the edges and corners if need be.
Poke the dough all over with a fork, then spoon the tart jam or jelly onto the dough and spread evenly right to the edges with a spatula. Remove the streusel from the fridge and distribute it evenly over the jam. Gently press down on the streusel to help it adhere to the jam. Cover with a tea towel and put it back in a place without drafts and allow it to proof again until it has risen in volume by 50%. This will take approximately 40 minutes at room temperature (21C, 70F). Preheat the oven to 325 degrees F.
Once the dough has risen, bake for 30 minutes or until the edges are a light golden brown. Remove and allow to cool on the baking sheet for 30 minutes before transferring to a cooling rack. Cut the cake into wide strips (easier for dunking in coffee) or any shape you like before serving.