Preheat oven to 325 degrees. Set aside an 8"x8" pan.
Mix together bread cubes and raisins in a large bowl.
Whisk milk, eggs, sugar, vanilla, melted butter and cinnamon in another bowl. Pour over bread mixture and stir in, mashing bread cubes with back of spoon to encourage them to sop up milk mixture. Mash and mix until bread is nice and soggy. (The crust pieces will hold their shape, but the cubes from the center of the loaf should disintegrate into a soggy bread mass. If there is more than 1/2" of milk mixture pooled on the bottom, you have too much liquid: add about 1/2 cup more bread cubes. If some of the bread cubes are still dry, add a little more milk.)
Pour mixture into pan and bake for 1 hour 30 minutes This is a good time to prepare your custard, make dinner, or ponder one of life's great mysteries. You may have to lay a sheet of foil over the top of the pudding in the last 30 minutes of cooking to keep it from browning too much.
Once it's set in the center (i.e. no longer mushy, but firm), remove from oven and allow to cool about 30 minutes until just warm. Slice into 9 blocks and serve warm, preferably with vanilla custard.
Variation 1: You can use any kind of bread you want, provided that it is a yeast bread, isn't sourdough, rye or pumpernickel, does not contain savory items (like rosemary. cheese or olives), and isn't overly salty. Other than that, use your imagination! Whole wheat breads are best when mixed with at least 1/3 white flour breads. This keeps the pudding from becoming too heavy. Mildly sweet breads, or those containing fruit or nuts, are also nice (think raisin bread or cinnamon bread.) Gluten-free bread can also be substituted with equally successful results.
Variation 2: Add 1/2 cup chopped nuts (hazelnuts are particularly nice).
Variation 3: Substitute any type of dried fruit for the raisins (cranberries, cherries, figs, currants, etc.)
Variation 4: Honey Orange Apricot Bread Pudding: Reduce sugar to 1/3 cup and add 2 tablespoons honey, 1/4 cup orange juice and zest of 1 orange to milk mixture. Omit cinnamon. Substitute 3/4 cup chopped dried apricots (I prefer the darker, more tart Blenheim variety than the Turkish ones, but both will work.).
Variation 5: Substitute 3/4 cup semisweet chocolate chips for the raisins. Serve drizzled with warm chocolate sauce.