Often, the “fluffiness” or “denseness” of a brownie is the product of the mixing method. In my experience, brownies made by hands by the method in these two recipes–melting chocolate and butter, stirring in sugar, then eggs, then the dry ingredients–are more fudgy and dense than brownies made by creaming together the fat and sugar as the first step. The less air whipped into a brownie, the more dense/fudgy the end result.

As to whether the brownies are similar, unsweetened chocolate contains more chocolate per ounce than semisweet chocolate (part of the ounce of semisweet is taken up with sugar), so brownies made with unsweetened chocolate tend to be more chocolatey than brownies made with semisweet chocolate. For me, the recipe using unsweetened chocolate is a more grown-up brownie. The recipe based on semisweet is more kid-friendly (sweeter and less deeply chocolate).

It’s really hard for me to say when brownies are “done.” If you’re looking for a dense, fudgy brownie, you’ll want to underbake them slightly. The longer they bake, the “cakier” they get as all the proteins in the eggs coagulate and the moisture evaporates out. As a starting point, try baking at 325F for about 30 minutes. Test them by poking them in the center of the pan with a toothpick. If it comes up wet and gooey, give them a few more minutes. If it comes up with wet crumbs, you’re there. There’s really no way to be more specific than that, but again, this gives you a place to start.