In a large bowl combine the yeast, 2 cups flour, baking powder and salt. Stir together and then add the butter and milk. Use a spatula to stir until a shaggy dough has formed.
Turn the dough onto a lightly floured surface and knead until the dough is smooth and elastic, adding more flour as needed (I added another ½ cup.)
Transfer dough to a lightly buttered bowl and cover with a clean dish cloth. Place somewhere warm and let proof for 30 minutes or until puffy and doubled in size.
Meanwhile stir together the brown sugar & filling spices and set aside.
Prepare a mega muffin tin by buttering each well. Set aside.
When the dough has proofed. Roll it to a 9x12 rectangle on a floured surface. Spread with the butter and then evenly sprinkle the filling all over. Roll the dough, starting on one of the short ends. Pinch to seal.
Use a serrated knife to cut into 6 equal pieces. Place each roll into a muffin tin well. Cover with the cloth and allow to proof for another 20-30 minutes or until doubled (They will be totally poofy at this point.)
Bake at 375F for 15 minutes or until golden brown.
For the glaze:
Whisk together the melted butter, powdered sugar, cardamon & milk. Add a teeny bit more milk if needed to reach drizzling consistency.
Serve warm.
Notes
I made these in a mega muffin tin, yielding 6 large buns. You could also use a regular 12-well muffin tin or even a 8x8 baking pan.
Recipe by The Baker Chick at https://www.thebakerchick.com/chai-spice-cinnamon-rolls/