1. Prep your ingredients: Remove the shells and devein shrimp; season with salt and pepper. Fill a small pot halfway with oil and bring to medium-high heat.
2. In a bowl, whisk together the flour, baking powder, dry mustard, and a pinch of salt. In a separate bowl, whisk together 3/4 cup of beer, 1 egg, and a tbsp. of oil.
3. Mix the wet ingredients into the dry ingredients using a spoon. Add more beer until it is your desired consistency.
4. When your oil is hot enough -- approximately 350 degrees or higher -- dip your shrimp into the beer batter, shaking off the excess, and gently drop into the hot oil. Cook no more than 4 at a time.
5. Once the batter is golden brown and the shrimp is opaque, lift from the oil and let cool on a paper towel-lined plate. Repeat until all of the shrimp is cooked.
6. Squeeze with fresh lemon juice and serve while the shrimp is still warm.