Danish pastry is in the same family of doughs as croissants and puff pastry. A lightly sweetened yeast dough has butter folded in, creating a rich morning treat.
Mix the water, yeast and flour together by hand in a large mixing bowl, or in the bowl of a stand mixer (fit it with the dough hook for the next step). Let this stand for 5 minutes.
Add the all-purpose and cake & pastry flours to the sponge, along with the sugar, salt and ¼ cup (60 g) of the butter. Mix this using electric beaters (with the hook attachments) or in the stand mixer on low speed until the flour is blended in, then increase the speed by one level and mix, adding the remaining 1 cup of butter pieces, a little at a time, until the dough feels elastic but most of the butter pieces are still visible, about 2 minutes. Cover the bowl and allow this dough to rise for 30 minutes, then chill for at least 2 hours.
On a lightly floured surface, turn the dough out and dust with a little flour. Roll the dough out to a rectangle about 18-inches (45 cm) long and 10-inches (25 cm) wide. Bring the two short ends of the dough to meet in the centre, then fold the dough in half at the point where they meet (this is called the book fold). Chill the dough, covered, for just an hour.
After the first hour, bring the dough out and roll it again into a rectangle 18-x-10-inches (45-x-25-cm), turn the dough over and fold it into thirds. Cover and chill for an hour. Repeat this step again one more time, then cover and chill at least 4 hours or overnight.