Whisk the flour, brown sugar, cocoa powder and salt in a medium bowl. Whisk the egg yolks, vegetable oil, coffee and coffee extract in another medium bowl. Whisk the egg mixture into the flour mixture until smooth. Divide the batter among four 10-ounce microwave-safe coffee mugs.
Microwave the mugs, one at a time, until the brownies are slightly firm and puffed, 1 1/2 minutes. Pour 1 tablespoon liqueur over each brownie when it comes out of the microwave. Set aside to cool slightly and let the liqueur soak in, at least 10 minutes.
Meanwhile, combine the heavy cream and confectioners' sugar in a medium bowl. Beat with a mixer on medium-high speed until medium-stiff peaks form, 1 to 2 minutes. Beat in the remaining 1/4 cup liqueur until just combined (do not overbeat). Top the brownies with the whipped cream and dust with cocoa powder.