Heat 1 tbsp (15 ml) butter in small saucepan.
Cook onion and garlic 3 minutes over medium heat.
Mix in paprika and continue cooking 1 minute.
Remove and puree in food processor; set aside to cool.
Mix onion mixture, remaining butter, lemon juice, salt and pepper together until well incorporated.
Slice bread and toast in oven.
Spread butter over pieces of bread and top with roast beef.