Making the McDonald's Filet-O-Fish Sandwich At Home | But Better

Bread:

1. Preheat oven to 375°F (190°C). Make the tangzhong by combining flour, water, and milk in a small saucepot. 
2. Whisk constantly over medium heat until it thickens into a smooth paste. Set aside to cool. 
3. In a separate bowl, mix warm milk and water. Stir in the yeast and let it sit until foamy (about 5–10 minutes).
4. In the bowl of a stand mixer, whisk together bread flour, sugar, and salt.
5. Add the oil, tangzhong, egg, egg yolk, and yeast mixture. 
6. Using a dough hook, knead on medium speed until smooth and elastic (about 10 minutes). Cover the bowl and let rise in a warm spot until doubled—about 1 hour.
7. Punch down the dough and turn it onto a lightly floured surface.
8. Divide into 9 equal pieces (about 80g each). Place buns on a parchment-lined baking sheet, evenly spaced.
9. Cover loosely with an inverted baking sheet or plastic wrap. Let proof for 30 minutes at room temp.
10. To shape: Gather the edges of each dough ball toward the center, flip seam-side down, and gently roll into a smooth ball on the counter using your hand. Whisk 1 egg with 1 tsp water. Brush the tops of each bun thoroughly. 
11. Bake buns for 15 - 18 minutes, or until deeply golden, puffed, and perfect. 
12. While still hot, brush the tops with melted butter for extra shine and richness. Transfer buns to a wire rack and cool completely.

Sauce:

1. mix all ingredients together in a large bowl until thoroughly combined.

Fish:

1. Cut the fish into 4 equal pieces about the size of the buns. Season generously with kosher salt and let sit for 10 minutes at room temperature.
2. For the batter, mix together the dry ingredients before whisking in 1 egg and beer. Whisk until fully combined.
3. Fill a large pot with oil to fill ¾ of the pot. Heat over medium heat until it reaches 365℉.
4. Fully coat fish with flour followed by the batter and into frying oil for 3-5 minutes. Drain fish on a wire rack in a lined baking sheet. Repeat with the remaining fish.
5. Slice the bun(s) in half and toast in butter. Top the bottom with cheese and optionally lightly melt with a kitchen torch.
6. Place the fish on top of the cheese with a dollop of tartar sauce before finishing with the top bun.