Step 1

In a large saucepan, toast the almonds, rice, and cinnamon over medium heat, stirring frequently, until the almonds are slightly golden and the cinnamon is very fragrant, 3 to 4 minutes. Add the half-and-half, stir to combine, and bring to a simmer. Remove from the heat, cover, and allow to steep for 2 hours.

Step 2

In a blender, working in two batches, puree the almond mixture until the nuts are pulverized and resemble a coarse flour. Pour each batch through a fine-mesh strainer set over a bowl and press down on the solids with a spatula or spoon to extract as much liquid as possible; discard the solids in the strainer. Blend the liquid in batches and strain once more; discard any solids left in the strainer.

Step 3

Partially fill a large bowl with ice and water, place a medium bowl in the ice water, and set the fine-mesh strainer across the top.

Step 4

Return the strained liquid to the saucepan and bring to a simmer over medium heat. Meanwhile, in a heatproof bowl, whisk together the egg yolks and sugar. Gradually ladle in about half of the hot liquid while whisking continuously. Whisk this mixture into the liquid in the saucepan and cook, stirring continuously, until the custard is thick enough to coat the back of the spoon. Pour the custard through the strainer into the prepared bowl, add the salt and vanilla, and stir until cool. Remove the bowl from the ice bath, cover, and refrigerate until the custard is cold, at least 3 hours or up to overnight.

Step 5

Whisk the custard to recombine. Freeze and churn in an ice cream maker according to the manufacturer's instructions. For a soft consistency, serve the ice cream right away; for a firmer consistency, transfer it to a container, cover, and allow to Harden in the freezer for 2 to 3 hours. Serve the ice cream sprinkled with ground Mexican cinnamon.