Step 1Add the yeast and 1 teaspoon of sugar to the warm water, whisk and let stand for 5 minutes.
Step 2In the large bowl of an electric mixer, combine the butter, the remaining 1/2 cup of sugar and the salt. Scald the milk by heating it in the microwave 2 minutes (or heat it in a saucepan until small bubbles form around the edges), then add it to the mixing bowl and slowly whisk until the butter is melted. Cool the mixture to lukewarm. Add the dissolved yeast and mix well.
Step 3Add 2 cups of flour and the ground cardamom and mix on medium speed until smooth, about 1 minute. Beat in the eggs 1 at a time. Add the remaining flour, 1 cup at a time, mixing 1 minute after each addition.
Step 4Scrape the soft dough onto a lightly floured board. Knead until you have a smooth and elastic dough, 6 to 7 minutes. You can also use the dough hook attachment and knead 5 to 6 minutes. When kneading by hand, it's OK to use an additional 1/4 cup flour for your hands and the board.
Step 5Place the dough in a greased bowl, cover and place the bowl in a warm place until the dough is doubled in size, about 1 hour.
Step 1Heat the oven to 325 degrees. Grease 4 baking sheets and set aside.
Step 2Toast the pecans on a dry baking sheet until lightly browned, 5 to 7 minutes. Finely chop them and place them in a bowl. Increase the oven temperature to 350 degrees.
Step 3Melt the butter and place it in a bowl. Put the sugar in another bowl.
Step 4Divide the dough into 4 pieces and roll each piece into a 12-inch log shape. Cut each log into 10 pieces. Roll each piece into a 6-inch rope. Fold each rope in half and cross each end over the other to form a braid shape. Place each braid on a baking sheet. Finish with the remaining dough. Dip each braid into melted butter, then into the bowl of sugar to coat, then place back on the baking sheets. Generously sprinkle each braid with nuts. Sprinkle with sparkling sugar, if using.
Step 5Bake the buns until they're pale golden, about 15 minutes. Remove them to cooling racks and cool completely. They will stay fresh in an airtight container at room temperature 2 to 3 days, or they may be frozen up to 1 month.