In stand mixer bowl, combine flour and salt. Use the flat or flex edge beater to mix them together.
In large liquid measuring cup gently whisk together eggs, oil and any flavor add-ins. (see below for Spinach and Tomato directions.)
On low speed, drizzle in the egg mixture.
Once the mixture starts to come together, switch to the dough hook and knead for about 3-5 minutes on speed 2.
The dough should be fairly stiff and a bit drier than some other doughs (pizza, sweet rolls…). If it’s very crumbly and not coming together add a little water a teaspoon at a time, but give it time to absorb after each teaspoon of water, it can get too wet very quickly. It will hydrate more as it rests in the refrigerator. Alternatively, If the dough seems to wet, add additional flour 1 tablespoon at a time. (The tomato paste and spinach puree versions especially may need a little more flour. I usually need to add at least 1/4 cup, even more with spinach version.)
Wrap dough in plastic wrap and rest for 20 minutes at room temperature or refrigerate overnight.
Make the Spinach Puree: Puree the thawed spinach (not squeezed dry yet) in food processor or blender. Then press the puree into a fine mesh strainer (if not fine enough, line with cheesecloth) to remove liquid Measure out 3-tablespoons of the mixture and add this to egg mixture.
Whisk the tomato paste into the egg mixture.
To Make in Food Processor - Use the dough blade. Pulse together all your dry ingredients. Whisk together the eggs, tomato paste and oil. With unit running on high speed, slowly pour in the wet ingredients. Mix until the mixture resembles pebbly texture. Pour out onto plastic wrap. Press mixture together into a disc shape. If mixture is too dry to hold together, you can sprinkle with a little water and knead by hand for a few turns. Wrap in plastic wrap and rest in refrigerator for at least an hour or overnight. Then roll and cut pasta.
Nutrition (approx. data estimated via online nutritional calculator.)