Toast the seeds: Place the sesame seeds, poppy seeds, flax seeds, and caraway seeds in a skillet. Cook over medium-low heat, stirring often, until the sesame seeds have turned golden brown, about 10 minutes. Remove from the heat and cool., To make the dough: In a large bowl, stir yeast into water to soften. Add honey, salt, shortening and cooled seeds. Weigh your flour; or measure it by gently spooning it into a cup, then sweeping off any excess. Add 2 cups flour to the yeast mixture., Beat vigorously for 2 minutes. Gradually add flour, a little at a time, until you have a dough stiff enough to knead., Turn dough out onto a floured surface. Knead, adding flour as necessary, until you have a smooth, elastic dough., Leave the dough on work surface. Cover with a towel and let rest for 10 minutes., Divide the dough into 12 equal pieces. Shape each piece into a ball. Cover the balls with a towel and let rest for 5 minutes., Lightly grease or line a baking sheet with parchment paper., Flatten each ball into a 3 1/2" circle. Make them slightly concave in the center. Place 1/2" apart on the baking sheet., Brush the tops lightly with vegetable oil, and lay a piece of plastic wrap over the buns. Cover the wrap with a cloth towel., Refrigerate for 12 to 24 hours., When you're ready to bake the buns: Preheat the oven to 400°F. Remove the buns from the refrigerator and let sit, covered, at room temperature., Bake for 20 minutes, or until done. Immediately remove buns from baking sheet and cool on a rack., Store, well-wrapped, for 4 days at room temperature, or freeze for up to 3 months.