Gather all ingredients, and preheat the oven to 425 degrees F (220 degrees C). Line a baking sheet with a silicone liner.

Combine butter, beer, salt, and sugar in a saucepan over medium-high heat. Let butter melt and bring to a simmer.

Add flour all at once and stir with a wooden spoon until it all comes together, about 30 seconds. Continue to cook and stir until the dough dries out a bit and starts sticking to the bottom of the pan, another minute or so.

Turn off the heat and continue stirring for another 1 to 2 minutes, scraping as much off the bottom of the pan as you can.

Transfer dough into a bowl. Add one egg and whisk it into a bit of the hot dough. Keep whisking in more dough until incorporated. Repeat with remaining egg until well combined and dough is sticky.

Add ? cup Cheddar cheese and cayenne and stir until incorporated.

Scoop 12 rounded tablespoons of dough onto the prepared baking sheet. Press a little Cheddar on the tops and sides of each puff.

Bake in the center of the preheated oven until nicely puffed and beautifully browned, about 25 minutes. Turn off the oven and crack the door; let cheese puffs cool, undisturbed, for 30 minutes.

Meanwhile, make the spread: Heat olive oil in a pan over medium heat. Add leek and ? teaspoon salt; cook and stir until just barely tender, 7 to 10 minutes, adding a splash of water every few minutes to prevent browning.

Stir in green onions and saut? briefly for 1 to 2 minutes. Transfer leek-onion mixture to a bowl and let cool for 5 to 10 minutes.

Add lemon juice and mascarpone cheese and mix until well combined. Season with salt and pepper to taste. Refrigerate until cheese puffs have finished cooling.

Serve cheese puffs with spread.