In the bowl of a stand mixer, whisk together the bread flour, sugar, salt, yeast, and spices/seeds. Using the dough hook, turn the mixer on low and slowly pour in the milk and melted butter. Increase speed to medium high and knead for 5 minutes.
Remove the dough hook and cover the bowl with plastic wrap. Place the bowl in a warm, draft-free area to proof (rise) for about 2 hours, or until doubled in size.
Refrigerate for at least 4 hours, but preferably overnight (the longer the dough is chilled, the easier it is to work with). Dough can be left in the refrigerator for up to one week.
On baking day, remove the dough from the refrigerator and dump onto a heavily flour surface. Knead gently until somewhat smooth. The dough is very sticky and loose, so use a bench scraper to help. Cut it in half with the bench scraper if you want to make two smaller loaves. You can also place half of the dough back in the fridge to bake fresh bread on another day.
Shape the dough into a torpedo shape and place it on a parchment-lined baking sheet or pizza peel (paddle). Cover with plastic wrap and place it in a warm, draft-free area to rise. It won't rise to double in size, just noticeably larger and puffy.
While the dough is rising, place a baking steel or baking stone on the middle rack of your oven and a shallow pan on the bottom rack. Preheat the oven to 450°.
When dough has fully risen, use the pizza peel (paddle) or the baking sheet and slide the dough onto the baking steel (or stone), parchment and all. Immediately pour one cup of very hot tap water into the shallow pan and close oven door. Bake for 30-35 minutes, or until the bread sounds hollow when tapped and is nicely risen. For a larger loaf (using all of the dough) add 5-10 minutes to the baking time. If the top is getting too dark before bread is done baking, cover lightly with aluminum foil.
Remove the bread from the oven and place on a wire rack. Allow to cool completely before slicing.
TO MAKE THE REUBEN:
Spread two pieces of gluten free mock rye bread with Russian dressing (or Thousand Island). Top one slice with corned beef followed by sauerkraut and Swiss cheese. Place other piece of bread on top and spread with softened butter.
Place buttered-sided down in skillet over medium-low heat. Spread other slice of bread with softened butter. Griddle sandwich until browned on one side and then flip over to brown the other side and allow cheese to melt slightly.
Remove from skillet and serve immediately.
To freeze, slice bread and place slices on parchment-lined baking sheet in a single layer. Flash freeze until each slice is solid. Wrap slices in plastic wrap and place in large ziptop bag and freeze for 2-3 months. Remove individual slices and wrap in plastic wrap or place in small baggie to thaw. Frozen bread may be toasted from frozen, however.
***DISCLAIMER: The reason I created my own flour blends is because I could not obtain the results I wanted with flour blends that were available in stores, online, or from other gluten free bloggers. My recipes have been developed to be used with my own bread flour blend that I created after painstakingly testing for, in some cases, YEARS to develop what I believe to be a superior gluten free bread like no other. If you do not use my gluten free bread flour blend for this recipe, I cannot speak for the results you will obtain. While store bought blends may give you a satisfactory result, they may NOT give you the results intended in my recipe.