In a saucepan, melt the butter over medium heat. Continue to cook the butter for about 5-7 minutes, swirling the pan occasionally, until nutty brown solids form at the bottom of the pan. Immediately remove from the heat, scrape the solids off the bottom of the pan with a spatula, and pour the butter into the batter.
Meanwhile, in a large bowl, whisk together the flour, brown sugar, baking powder, baking soda, salt and spices.
When the browned butter is ready, pour the butter into the bowl of dry ingredients, and add the buttermilk, eggs and vanilla. Whisk briefly to combine. Fold in 1/2 cup of the chopped pecans. The batter will be thick and fluffy.
Preheat a griddle to 300F and lightly grease with butter. Use a cupcake scoop, or a 1/4 cup measuring cup, to portion out the batter, leaving several inches between each. The batter is very fluffy and won't spread on its own, so immediately after scooping it onto the griddle, use a spatula to gently spread it out a little.
Cook the pancakes until golden brown underneath, and they can be easily flipped. Flip over, and cook the other side until they are cooked through.
Serve with the toffee butter sauce and the rest of the chopped pecans.