Melt butter in a skillet set over medium heat and add chopped onion.
Caramelize the onion while stirring infrequently, scrapping any burnt on fond on the bottom of the pan so it can incorporate into the onion as it cooks. When the onion is threatening to burn, drop the heat to low while it finishes caramelizing. Add garlic in the final few minutes of cooking. Expect caramelizing the onion to take approximately thirty minutes.
Add ¼ cup of water to the skillet and scrape off any burnt-on bits from the bottom of the skillet and stir them into the onion. Continue to cook until all of the water has evaporated or absorbed into the onion.
While the onion is caramelizing break apart the trout into smaller pieces, being careful to remove all bones.
Prepare the dip by whisking together softened cream cheese and sour cream in a large bowl. Then add Worcestershire sauce, smoked trout pieces, lemon juice, and fresh ground black pepper. Stir in caramelized onion and garlic when it has finished cooking.
The flavor will be best if this dip is allowed to chill in the refrigerator for a few hours prior to serving. Serve this creamy dip with your favorite crackers, chips, or bagel chips.