For the hollandaise sauce: Melt the butter over low heat in a small pot - do not let it boil. In a bowl, whisk the egg yolks and lemon juice; season with salt and pepper. Slowly drizzle in the melted butter while whisking. Continue whisking until the sauce becomes nice and thick. (The sauce should be thick, buttery, lemony and just lightly salty. If it is not salty or lemony enough, you can add a little lemon juice or salt to taste.)
Fill a sauté pan halfway with water. Bring the water to a low simmer.
Stir the vinegar into the water.
Crack the eggs into a bowl. Gently place the eggs into the water. (You can poach multiple eggs at once, being careful not to overcrowd the pan.)
Cook the eggs in the water for 3-5 minutes gently flipping over about halfway through until the whites are firm. Remove the eggs with a slotted spoon onto a paper towel to drain excess water.
While the eggs are cooking, brown the chicken sausage on both sides in a non-stick pan over medium heat.
Toast the bread. Spoon the hollandaise sauce over the eggs. Season with salt and pepper. Serve with chicken sausage and raspberries.