Step 1: In a small bowl, combine the warm milk, sugar, and active dry yeast. Stir gently until the sugar dissolves, then let the mixture sit for 5-10 minutes. You'll see a foamy layer on top, confirming your yeast is active.
Step 2: In a larger mixing bowl, whisk together the sweetened condensed milk, melted unsalted butter, large egg, and optional vanilla extract until everything is smooth and thoroughly combined.
Step 3: Pour the activated yeast mixture into the bowl with the wet ingredients. Stir well to fully integrate all components.
Step 4: Gradually add the all-purpose flour and salt to the wet mixture. Stir with a wooden spoon or a sturdy spatula until a shaggy, cohesive dough starts to form.
Step 5: Transfer the dough to a lightly floured surface. Knead by hand for about 5-7 minutes, or use a stand mixer with a dough hook on medium speed for 4-5 minutes, until the dough is smooth, elastic, and no longer sticky.
Step 6: Lightly grease a large clean bowl with oil. Place the kneaded dough in the bowl, turning it once to coat. Cover the bowl with a clean kitchen towel or plastic wrap and let it rise in a warm, draft-free spot for approximately 1 hour, or until it has visibly doubled in size.
Step 7: Once the dough has doubled, gently punch it down to release the trapped air. Turn the dough onto your floured work surface and carefully shape it into a neat loaf.
Step 8: Grease a standard 9x5-inch loaf pan. Transfer the shaped dough into the prepared pan. Cover again and allow it to rise for a second time, for 30-40 minutes, or until it has risen nicely above the rim of the pan.
Step 9: While your dough is on its second rise, preheat your oven to 350°F (175°C).
Step 10: Bake the bread in the preheated oven for 25-30 minutes, or until the top is a beautiful golden brown and the loaf sounds hollow when gently tapped on the bottom.
Step 11: Remove the baked bread from the oven and let it cool in the loaf pan for about 10 minutes. Then, carefully transfer it to a wire rack to cool completely before slicing and serving. This cooling process helps achieve the perfect texture.