Toast the raw nuts in the oven at 350°F for 5 minutes and stir. Toast for another 3 to 5 minutes, until fragrant but not dark.

Place the toasted nuts, garlic, fennel fronds, parsley, and salt in a food processor. Pulse to make a paste. Scrape down the sides of the food processor if necessary.

With the processor running, stream in the oil in a slow trickle, until the pesto is well blended. Transfer to a large serving bowl. (If not using immediately, refrigerate or freeze in a wide-mouth jar.)

Place the semolina in a large bowl and make a well in the center. Pour in the hot water. (Alternatively, you can make this directly on your work surface. For a beginner, you may prefer to use a bowl.)

With a fork, incorporate the flour from the edges of the well into the water. Continue until you’ve combined all the flour and water and have formed a crumbly dough.

Turn the dough out onto a floured surface. The bowl will likely contain enough unincorporated flour that you won’t need more on your work surface. Knead the dough until it is smooth and elastic. It should spring back after you make an indentation in it with your thumb. If it doesn’t spring back, keep kneading it. This can take about 10 minutes. Cover with a clean dish towel and let rest for 20 to 30 minutes.

Dust the dough with semolina. Roll each piece of the dough up into a very loose tube (see the picture opposite). You will be slicing noodles from these tubes, so you don’t want it too tightly wound and stuck together. Cut 1/4-inch-wide noodles from each roll.

Add the salt to a large pot of water and bring to a boil. Add the noodles and cook until tender, about 2 minutes. Reserve at least 1/3 cup of the pasta cooking water. Drain the pasta in a colander.

Whisk the saved pasta cooking water into the bowl with the pesto. Blend and toss the pasta in the pesto and serve.