Preheat the oven to 375F, and line a 12 cup muffin pan with paper liners.
In a small saucepan, melt the butter over medium heat. Once melted, keep it over the heat until it starts to turn brown and smell nutty - keep an eye on it - little browned bits will appear in the bottom like a scrumptious sludge. Take it off the heat and set aside.
Whisk together the milk, egg, egg yolk and vanilla. In a larger bowl, stir together the flour, sugar, baking powder and salt. Add the butter mixture and stir until almost combined; add the berries and gently stir just until blended.
Mix the topping ingredients in a small bowl, using a fork or your fingers to blend until crumbly.
Divide the batter among the muffin cups. (Mine was thick enough to pick up wads with my fingers and press in, filling them pretty much up.) Sprinkle with the crumble and bake for 20-25 minutes, until golden and springy to the touch.