Cut the butter into 32 pieces and toss in a bowl with 1 tablespoon flour. Set aside.
In the bowl of a stand mixer combine 4 cups of flour, milk powder, sugar and yeast. Whisk until combined. Fit the mixer with the dough hook. Set the speed on medium-low and add the water and the egg. Continue to mix until a cohesive mass forms, about 2 minutes. Scrape down the sides of the bowl if needed. Cover the mixing bowl with plastic wrap and set aside in a warm location for 20 minutes. After 20 minutes the mixture should be a little bubbly and puffy.
Remove the plastic wrap from the mixer bowl and add the salt. Mix on medium low until the dough is smooth and elastic and just about clears the sides of the bowl; about 15 minutes. If needed at the end, add 1 or 2 tablespoons of flour and continue mixing until the dough ball clings to the hook and clear the sides of the mixing bowl. A little sticky dough in the bottom of the bowl is okay.
With the mixer running, add the butter, a few pieces at a time. Continue to knead until the butter is fully incorporated and the dough is smooth and elastic and clears the sides of the bowl, 3 to 5 minutes more. Add the raisins and mix until incorporated.
Transfer the dough to a large greased bowl. Using your hands, a bowl scraper or rubber spatula, fold the dough over itself by gently lifting the dough from underneath and folding the edge of dough toward the middle. Turn the bowl a quarter turn and fold again. Turn the bowl another quarter turn, and fold 6 more times for a total of 8 folds.
Cover tightly with plastic wrap and transfer to the middle rack of the oven. Place a loaf pan on the bottom of your oven. Pour 3 cups of boiling water into the loaf pan and quickly close the oven door. Allow the dough to rise for 45 minutes - no peaking!
Remove the bowl from the oven and gently press down on the center of the dough to deflate. Repeat the folding steps (for a total of 8 folds). Recover the bowl with plastic wrap and return the dough to the oven until doubled in size, about 45 minutes.