Whisk the large egg, water, oil, sugar and yeast together until the yeast is completely dissolved. Combine the two types of flour with the salt. Add ⅔ of the flour mixture to the wet ingredients and combine. Continue adding the flour mixture gradually until the dough is no longer sticky. Knead the dough well for about 5 minutes. Now add little squares of cold butter, kneading until incorporated into the dough.
Put the dough aside, cover with a tea towel and let rise for an hour. Move the dough to a worktop sprinkled with flour. Divide into 14-15 pieces of equal size. Roll each piece of dough into the shape of a hotdog bun and place on a baking sheet lined with baking parchment. Let rise for an additional 30 minutes. Brush the buns with the slightly beaten egg and sprinkle with sesame seeds.
Bake the buns at 200°C for 12-15 minutes. They should be slightly golden and sound hollow when tapped on the bottom.
Mash the cheese with a fork and combine with the remaining ingredients. Season to taste with salt and pepper.
Slice the tomatoes in half and arrange in a small baking dish. Sprinkle them with olive oil, salt and pepper. Bake at 150°C until slightly dried. Approx. 35-50 minutes, depending on their size. Bake extras and store in the refrigerator. Use them just as you would sun-dried tomatoes, for instance in salads.
Sprinkle the finely grated Gouda in a thin layer on a baking sheet lined with parchment. Bake at 150°C for 12-14 minutes. The duration depends on how finely the cheese is grated and how thick the layer is. It is done when the cheese is melted and slightly golden. Remove from the oven and allow to cool until crispy, then break up into smaller pieces.
Heat the buns. Roast the sausages. Top with some Castello Traditional Danish Blue cheese dressing, onion sprouts and tomatoes. Bon appetit! A remarkably delicious hotdog.