Special equipment: 2 silicone baking mats or parchment paper; a piping bag; a 3/8-inch round pastry tip
For the gougeres: Preheat the oven to 400 degrees F. Line two baking sheets with silicone baking mats or parchment paper.
In a medium saucepot combine the milk, sea salt, sugar and butter, and bring to a boil. Add the flour and cook until thoroughly incorporated, about 2 minutes. Transfer the mixture to the bowl of stand mixer fitted with the paddle attachment and mix until the dough is the temperature of warm tap water, about 30 seconds. Add the eggs, one at a time, until smooth. Fold in half of the gruyere and some pepper.
Transfer the batter to a pastry bag fitted with a 3/8-inch round pastry tip. Pipe 1-inch-wide rounds on the prepared baking sheets 2-inches apart, about 60 total. Sprinkle the top with the remaining gruyere and some black pepper.
Wet a fingertip and press down lightly to remove the point on each gougere. Bake for 8 minutes and rotate. Bake until the gougeres are golden brown, another 4 minutes. Cool to room temperature.
For the Mornay: In a medium saucepot set over low heat, melt the butter and sweat the shallots and garlic for 5 minutes. Season with salt and pepper. Add the flour and cook until it smells toasted, 2 minutes. Add the milk and bring to a boil, stirring continuously so no lumps form. Reduce the heat to a simmer and cook until the sauce reaches the desired consistency. Slowly add the gruyere and Parmigiano-Reggiano, and stir until smooth. Add the mustard and season with salt and pepper. Transfer the Mornay to a bowl and cool in the fridge or set over ice. When cool, transfer to a piping bag fitted with a small tip.
For the sauce: In a large bowl, combine the mayonnaise, mustard, beer extract powder, honey, mustard powder and vinegar, and whisk thoroughly to remove the lumps. Season with salt and pepper.
Preheat the oven to 350 degrees F.
Fill the gougeres with the Mornay sauce and reheat in the oven to melt the cheese, 5 minutes. Serve the hot gougeres with the beer mustard.
Don't be afraid to achieve a very caramelized and golden color on the pastry. The bitterness works well with the cheese and the creamy sauce. The sauce should be made to taste mostly. If you prefer a creamier sauce, use more mayonnaise. If you prefer something spicier, use more mustard. I also like to fold in a touch of truffle oil to make the dip very special for the season.