Preheat oven to 175°C. Melt butter and brush pan with half of it. Add peanut butter to remaining melted butter and heat over low heat until fluid.
Remove from heat and whisk in milk, then whisk in egg yolks, eggs, sugar and vanilla. Toss mixture with diced bread and let sit 10 minutes.
Spoon mixture into prepared pan and dollop jam over bread, pressing in slightly to incorporate just a touch. Sprinkle with Turbinado sugar.
Place pan in a larger dish and fill it with an inch of hot tap water. Bake for about 50 minutes, until golden on top and set. Let pudding sit for at least 30 minutes before serving.
Pudding can be served warm or chilled.