Special equipment: 16 shot glasses
Pour 1/2 cup of the beer in a medium bowl. Sprinkle the gelatin over the beer and let it dissolve, about 1 minute.
Combine the granulated sugar and remaining 1 1/2 cups beer in a small saucepan. Heat over low heat until the sugar dissolves and the liquid is steaming but not boiling. Pour over the dissolved gelatin and stir to melt the gelatin completely. Strain the mixture into a spouted measuring cup and pour into 16 shot glasses. Refrigerate until set, about 2 hours.
When ready to serve, whip the cream and confectioners' sugar with an electric mixer in a medium bowl to form soft peaks. Whisk in the tequila and lime zest. Dollop the tequila-lime whipped cream on top of the beer shots to resemble the foam head on a beer. Garnish the sides of the glasses with lime wedges.