In a bowl, whisk together flour, sugar, yeast, and salt.

Working quickly, rub the butter evenly into the flour mixture. Do this by hand or by using a pastry blender.

In a small bowl, whisk egg, milk, and vanilla together, then pour into the flour mixture.

Mix quickly into a dough, handling as little as possible so as to not melt the butter. You want to still see the pieces of butter throughout.

Shape the dough into a small rectangle, wrap in plastic wrap, and chill for at least 3 hours or overnight.

Once the dough has chilled and rested, on a floured surface, roll the dough out to a large rectangle, about 8 x 15 inches (20 x 28 cm).

Fold the dough in thirds, like a letter, so that the dough is in 3 layers (see video above.)

Re-flour your surface if needed, and then re-roll the dough into a large rectangle, turn it, and re-fold into thirds.

Repeat this rolling, turning, and folding one more time, then wrap the dough in plastic wrap and refrigerate for 1 hour.

After the dough has been rested and chilled for an hour, repeat the rolling and folding process 1 more time: Roll, turn, and fold 3 more times.

Wrap the dough well and refrigerate for at least 2 hours and up to 2 days. For longer storage, this dough can be frozen, well wrapped or in an airtight container, for up to 1 month. Defrost overnight in the refrigerator before using it.

In a bowl, mix together granulated sugar, brown sugar, cinnamon, and salt. Set aside.

Butter a 12-cup muffin tin generously with melted butter. Set aside.

On a floured surface, roll danish dough into a 12 x 18 inch (30 x 45 cm) rectangle.

Brush the dough with the softened butter. Make sure to use ALL the butter.

Sprinkle all the cinnamon-sugar mixture evenly over the dough, leaving a small, 1-inch (2 1/2cm) border on one narrow end unsprinkled.

Just like a cinnamon roll, starting with the widest side, gently roll up the dough into a log.

With a serrated knife, slice the roll into 10-12 equally-sized pieces and place, cut side up, in the muffin tin cups. (If you do 10 buns instead of 12 you get much bigger buns)

Cover the dough and let rise in a warm place until puffed, about 60 minutes. Tip: I preheat my oven for 2 minutes, then turn it off and place it in the tray of buns. This warmth gives them a great environment to proof well.

At the end of the rise time, preheat the oven to 375°F (190°C).

Uncover the dough and bake until golden brown, about 20-25 minutes. You might notice some melted butter around your rolls and that is ok, don't worry. That will bake into the buns and just make an incredible, buttery dough.

Let cool in the tin for 10 minutes before removing to a wire rack to cool completely.

These buns are best the day they are made, but you can store any leftovers in an airtight container at room temperature overnight or in the refrigerator for up to 3 days. Rewarm in the microwave or in a 300°F (150°C) oven for 10 minutes.