To prep

Line the bottom of a 13- by 9-inch baking pan with foil or parchment paper. Grease foil or parchment paper and sides of the pan with baking spray. Also, grease a medium bowl to hold the dough when it’s completed.

For the dough

1. Whisk warm 110 degree milk and yeast in liquid measuring cup until yeast dissolves. Then whisk in eggs, and vanilla extract. In bowl of stand mixer fitted with dough hook, mix flour, cornstarch, sugar, and salt until combined. With mixer on low, add warm milk mixture in steady stream and mix until dough comes together, about 1 minute. Increase speed to medium and add butter, one piece at a time in 10-second intervals until incorporated. 
2. Continue to mix until dough is smooth and comes away from sides of bowl, about 10 minutes. If after mixing for 10 minutes the dough is still wet and sticky, add up to 1/4 cup flour (one tablespoon at a time) until the dough releases from the bowl. Turn dough out onto clean surface and knead to form a smooth, round ball.
3. Transfer dough to prepared bowl, cover with plastic wrap, and place in turned off oven with oven light on (it allows enough gentle warmth). Let rise until doubled in size, about 2 hours.

For the filling

1. In a medium stainless steel saucepan, melt 6 tablespoons of unsalted butter over medium-low heat until it starts to brown, about 4-6 minutes. Don’t walk away from this. As soon as it browns nicely, turn off the heat and add in 2 tablespoons of cold unsalted butter. Mix it around until the mixture cools down. Set aside and cool while the dough rises.
2. Combine brown sugar, cinnamon, and salt in small bowl using a fork or your fingers to break up any large lumps. Turn dough out onto lightly floured surface. Roll dough into 18-inch square. Leaving a 1-inch border, drizzle the brown butter all over the surface (you may not need all of it), and sprinkle evenly with filling. Lightly press the filling into the brown butter. 
3. Starting with the widest edge nearest you, roll dough into tight cylinder, pinch lightly to seal seam, and cut into 12 pieces using either a serrated knife or bench scraper. It’s easier to cut the dough in half, then cut each side in half until you have 12 rolls. You could also make 8 super large rolls, if you prefer. 
4. Transfer pieces, cut-side up, to prepared pan. Cover with plastic wrap and let rise in a turned off oven or warm spot until doubled in size, about 1 hour.

For the glaze and to bake

1. Heat oven to 350 degrees. 
2. In a medium stainless steel saucepan, melt 4 tablespoons of unsalted butter over medium-low heat until it starts to brown, about 4-6 minutes. 
3. Pour the hot brown butter over the powdered sugar, including as many brown bits as possible. Whisk brown butter and sugar together, then pour in the heavy cream in 1/4 cup increments until you reach a desired consistency. Add the vanilla, pinch of salt, and corn syrup (if using). Give it a final whisk and set aside. 
4. Discard plastic wrap and bake buns until deep golden brown and filling is melted, 30-35 minutes. Cool for about 10 minutes then pour over some of the glaze. You may not have to use all of the glaze, I didn’t. I stored the rest of the glaze in the freezer for later use. 
5. Serve.