Introduction:
The correct answer to the given question is option 'A' - breakfast. In this response, we will explain why breakfast is the correct answer and provide a detailed explanation.

Explanation:
- Bread, butter and egg: These three food items are commonly associated with breakfast. They are frequently consumed together in various breakfast dishes.
- Favourite: The word 'favourite' indicates a personal preference or choice. It suggests that the speaker enjoys eating bread, butter, and egg as a part of their regular breakfast routine.
- Breakfast: Breakfast is the first meal of the day, typically consumed in the morning. It is considered an important meal as it provides the body with energy to start the day and kick-starts the metabolism.
- Timing: Breakfast is usually consumed within a few hours of waking up. It helps replenish the body's glucose levels after an overnight fasting period and provides essential nutrients to support physical and mental activities throughout the day.
- Components: A typical breakfast may include a variety of food items such as bread, butter, eggs, cereal, fruits, and beverages like milk, tea, or coffee.
- Importance: Breakfast is often referred to as the most important meal of the day. It has been linked to various health benefits, including improved concentration, better memory, enhanced mood, and increased productivity.
- Nutritional value: Bread provides carbohydrates and fiber, butter contributes healthy fats, and eggs are a good source of protein and essential nutrients like vitamins and minerals.
- Variety: Breakfast can be enjoyed in various forms, such as toast with butter and scrambled eggs, a breakfast sandwich, or even a simple bowl of cereal with milk.
- Culinary traditions: Different cultures and countries have their own unique breakfast traditions and dishes. For example, in some regions, bread, butter, and eggs may be served with additional accompaniments like sausages, bacon, or vegetables.
- Personal preference: The phrase "my favorite" suggests that the speaker personally enjoys eating bread, butter, and egg for breakfast. It reflects their individual taste and preference.

Conclusion:
In conclusion, the correct word to complete the given sentence is "breakfast." This choice is supported by the fact that bread, butter, and eggs are commonly associated with breakfast, and the word "favorite" indicates a personal preference for consuming these items as part of the morning meal.