1. Put the bacon slices in a cool pan and fry until crispy over medium-high heat. Remove the bacon slices from the oil and let cool on paper towels. Reserve the leftover bacon fat in a bowl. Then finely chop the bacon.
2. Whisk the egg yolks with the mustard and white wine vinegar. Add the oil and bacon fat very slowly, whisking constantly. Stir in the bacon and season to taste with salt and pepper.
3. Peel and slice the onions and fry them in butter. When the onions are soft, add the sugar and let it melt. Stir in the wine and add the sprigs of thyme. Cook off the wine for approx. 15 min.
4. Peel the onion for the cucumber salad. Thinly slice the onion and the cucumber and place in a bowl. Combine the lemon juice, oil, rose pepper and salt. Pour the dressing over the onion and cucumber slices and stir gently.
5. Form four patties out of the ground meat. Sprinkle with salt and pepper.
6. Heat the grill, brush the grill grate lightly with oil and barbecue the meat for 2-3 min. on each side. Cover with the Castello® Burger Blue cheese and let melt. Toast the buns sliced-side down. Top each bun with a burger, bacon mayo, cucumber salad and onions in port wine.